Systems, devices and methods for the prevention and treatment of pressure ulcers, bed exits, falls, and other conditions

ABSTRACT

A system for monitoring medical conditions including pressure ulcers, pressure-induced ischemia and related medical conditions comprises at least one sensor adapted to detect one or more patient characteristic including at least position, orientation, temperature, acceleration, moisture, resistance, stress, heart rate, respiration rate, and blood oxygenation, a host for processing the data received from the sensors together with historical patient data to develop an assessment of patient condition and suggested course of treatment. In some embodiments, the system can further include a support surface having one or more sensors incorporated therein either in addition to sensors affixed to the patient or as an alternative thereof. The support surface is, in some embodiments, capable of responding to commands from the host for assisting in implementing a course of action for patient treatment. The sensor can include bi-axial or tri-axial accelerometers, as well as resistive, inductive, capacitive, magnetic and other sensing devices, depending on whether the sensor is located on the patient or the support surface, and for what purpose.

RELATED APPLICATIONS

The present application is a divisional of, and claims the benefit under35 USC Section 119 of U.S. patent application Ser. No. 13/070,189, filedMar. 23, 2011, and through it further claims the benefit of thefollowing applications: U.S. provisional Patent Application Ser. No.61/438,732, filed Feb. 2, 2011, entitled System for Optimizing PatientTurning; provisional Patent Application Ser. No. 61/326,664, filed Apr.22, 2010, entitled Methods and Devices that Enable the Sensing of BodySurface Markers for the Prevention and Treatment of Pressure Ulcers andOther Wounds; provisional Patent Application Ser. No. 61/411,647, filedNov. 9, 2010, entitled Method and Device for Surface PressureMonitoring; provisional Patent Application Ser. No. 61/393,364, filedOct. 15, 2010, entitled Patient Position, Orientation, and SurfacePressure Monitoring Device; and provisional Patent Application Ser. No.61/373,260, filed Aug. 12, 2010, entitled Sensing System thatAutomatically Identifies and Tracks Body Surface Markers to Allow forthe Delivery of Targeted Therapy. The foregoing applications are allincorporated herein by reference for all purposes.

FIELD OF THE INVENTION

Aspects of the present invention relate generally to systems, devicesand methods for the detection of compromised tissue perfusion and otherissues affecting the health of a patient, and more particularly relatesto systems, devices and methods for such detection, communicating ofrelevant information to a host, and providing either appropriateguidance to a caregiver to facilitate proper management of the patientor device instructions for providing automated care.

BACKGROUND OF THE INVENTION

The management of pressure ulcers poses a substantial burden to thehealthcare system. Each year, the United States spends billions ofdollars treating pressure ulcers and associated complications. Pressureulcers are very common and they represent a significant source ofmorbidity and mortality for patients. The prevalence of pressure ulcersin the US alone is estimated to be between 1.5 and 3.0 million people,with two thirds of cases involving patients 70 or older.

Pressure ulcers, which are also known as pressure sores, bed sores, ordecubitus ulcers, represent localized areas of tissue damage. Pressureulcers often occur when the soft tissue between a bony prominence and anexternal surface is compressed for an extended period of time. Pressureulcers can also occur from friction, such as by rubbing against a bed,cast, brace, or the like. Pressure ulcers commonly occur in immobilizedpatients who are confined to a bed, chair or wheelchair. Localizedtissue ulceration results when pressure on the skin exceeds capillaryfilling pressure (approximately 32 mm Hg), which thereby impedes themicro-circulation in the skin and the underlying subcutaneous tissue.With compromised blood flow, the delivery of oxygen and nutrients totarget tissues is impaired. If blood flow is not restored promptly, theskin and subcutaneous tissue will die and a pressure ulcer will develop.

Pressure ulcers will initially appear as areas of red or pink skindiscoloration, but these areas can quickly develop into open wounds ifleft untreated. Open wounds can lead to severe health complications byexposing patients to life-threatening infections. The primary goal inthe treatment and prevention of pressure ulcers is to relieve pressureon and around affected tissues. Pressure relief can be accomplished byfrequently changing the position of immobilized patients and by usingsupport surfaces that minimize surface pressure. Although pressuremanagement is the most critical aspect of any successful treatmentprogram, it is also important to ensure that patients receive adequatenutrition, engage in daily exercise, and follow a good skin care andpersonal hygiene protocol.

A Braden score is commonly used by caregivers to assess a patient's riskfor developing a pressure ulcer. The Braden scale is composed of sixcriteria, which when taken together, can be used to estimate a patient'slikelihood of ulceration and can also be used to determine the level ofpressure ulcer prevention procedures required for a specific patient.The six components of the Braden scale are: sensory perception,moisture, activity, mobility, nutrition, and friction/shear forces. Eachcomponent is rated on a scale of 1 to 4, with the exception offriction/shear which is rated on a scale of 1 to 3. The maximum score is23, and higher scores reflect a lower risk of developing pressureulcers. In general, patients with a Braden score of less than 18 areconsidered to be at high-risk for developing a pressure ulcer.

Various devices and methods for treating and preventing pressure ulcershave been developed. The cornerstone of pressure ulcer prevention is toturn patients on a regular basis, such as every one or two hours.Patients confined to a wheelchair, chair, or other surface should bemoved in such a manner. Intermittent relief of surface pressure hasproven to be highly effective in preventing the development of pressureulcers. However, various factors limit compliance withturning/repositioning protocols.

Alarm systems have been developed to help improve compliance withpatient turning/repositioning protocols. Generally, these alarms aretriggered when the system detects an inadequate amount of patientmovement over a predefined time interval. Movement can be detected usingvarious modalities, which include vibration sensors, pressure sensors,and video cameras. Although these systems can detect patient movement,they cannot reliably determine if the perceived movement resulted inadequate depressurization from specific regions of the body.

Also, current alarm systems cannot compute the cumulative pressure-timeindex (or pressure dose) at specific regions of the body. Although somealarm systems have been designed to measure the surface pressuredistribution over a support surface, they are unable to directlycorrelate the measured pressure with discrete regions of a patient'sbody. For example, although a pressure sensitive mat placed under apatient can measure the overall surface pressure, it cannotautomatically and directly measure the surface pressure at discreteregions of the body, nor can it directly track the cumulative pressuredose at specific regions of the body over time. Furthermore, pressuresensitive mats cannot easily and robustly distinguish between pressureresulting from patient contact with the support surface vs. pressureresulting from non-patient contact with support surface (i.e. books,food trays, etc.).

In addition to turning regimens, pressure ulcer prevention andmanagement also commonly involves the use of pressure reducing supportsurfaces, which are well known in the art. Such support surfaces attemptto minimize the overall surface pressure and some support surfaces, suchas alternating-pressure mattresses, are designed to modulate the surfacepressure as a function of time. Although it is desirable to minimize theoverall surface pressure, it is important to recognize that differentregions of the body have different surface pressure thresholds.

For example, areas underlying bony prominences, such as the hips andsacrum, have relatively low surface pressure thresholds, which is whypressure ulcers commonly occur at these locations. Support surfaces arecurrently not able to detect or differentiate among specific regions ofa patient's body. Without this detection ability, support surfaces arenot able to selectively modulate surface pressure at specific regions ofa patient's body. Also, current support surfaces cannot automaticallyidentify areas of compromised tissue perfusion, so they are unable toautomatically redistribute pressure away from ischemic areas.

There is a long-felt, definite and even urgent need for a system,method, and device that helps to prevent, detect, and/or treatpressure-induced ischemia and pressure ulcers by optimizing surfacepressure at areas of compromised tissue perfusion. Various aspects ofthe present invention accomplish these objectives and substantiallydepart from the conventional concepts and designs of the prior art.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byproviding systems, methods and devices for patient management, includingthe detection, treatment and prevention of wounds such as pressureulcers, among other things, and conditions likely to cause such wounds.Furthermore, the present invention provides communication from one ormore sensors monitoring a patient to a host system to alert caregiversto key conditions and to enable an improved, more reliable method forpatient care. Alternatively, the host system can initiate an automatedcare event. Some aspects of the present invention relate to sensingsystems that locate sites of compromised tissue perfusion or tissueinjury and substantially optimize surface pressure at those locations.

Other aspects of the present invention relate to sensing systems thatprovide information regarding the position, orientation, and/ormovements of a patient, and allow for surface pressure optimizationbased on this information. Here the position refers to the shape thatthe body takes independent of orientation, for example, knees bent, backstraight, arms above head. The orientation refers to direction that thebody is facing and the angle, for example, supine, prone, rotated left,rotated right, tilted Trendelenburg, tilted reverse Trendelenburg, etc.Movement refers to changes in either position, location, or orientation,achieved by bending, translating, or turning, respectively. Such sensorscan be placed directly on the body, or on or in the support surface, oron or in clothing worn by the patient, or can be sensors capable ofmonitoring patients from more remote locations. In a presently preferredarrangement, a sensor comprising a multi-axial accelerometer providesdata representative of patient position, orientation, and movement,which is then processed by a host system, which can be remote from thesensor, as described hereinafter

Other aspects of the invention provide techniques for selectivelymodulating surface pressure at and around sites of compromised tissueperfusion, or sites of tissue injury, or sites considered to be at riskfor developing tissue injury or sites where pressure is not desirable,thus substantially eliminating at least some of the conditions likely tolead to the formation of pressure ulcers, as well as aiding in thetreatment of pressure ulcers and other wounds.

Still other aspects of the present invention comprise the use of bodysurface markers together with systems and techniques for optimizingsurface pressure at locations corresponding to such body surfacemarkers. For example, body surface markers can be placed over areas ofdamaged tissue or areas thought to be at high-risk for developingpressure sores (i.e. hips, heels, sacrum, etc). The support system canthen attempt to focus pressure-relieving maneuvers at and around theselocations. Body surface markers can include, but are not limited to, thefollowing: stickers, wound dressings, socks, undergarments, and sensibleink or other media, films, or adhesives. Depending upon theimplementation, body surface markers can be comprised of anything thathas at least one sensible property that is in some way distinguishablefrom the patient by a host system. As used herein, “sensible” means“capable of being sensed.” In at least some embodiments of the presentinvention, pressure distribution over time and location is thenselectively optimized with respect to the body surface markers in aneffort to optimize tissue perfusion.

Still further aspects of the present invention are configured tominimize or eliminate physical contact with injured tissue, areas ofcompromised tissue perfusion, areas identified to be at-risk forcompromised tissue perfusion, or areas corresponding to body surfacemarkers. An objective of an embodiment of the present invention is tocontrol the surface pressure at sites of tissue injury, sites identifiedas having compromised tissue perfusion, or sites corresponding to bodysurface markers. These aspects of the invention allow for increasedblood circulation and increased airflow to critical areas, thuspromoting the healing of existing pressure ulcers and preventing theformation of other pressure ulcers.

THE FIGURES

FIG. 1 illustrates in block diagram form an embodiment of a system inaccordance with one aspect of the invention in which one or more sensorsprovide to a host data representative of a patient's position,orientation, and movement, and the host uses that information, togetherwith other patient information, to identify risks with respect to eitheravoidance or treatment of pressure ulcers on the patient, among otherthings.

FIG. 2A illustrates in block diagram form an embodiment of the hardwareof a system in accordance with one aspect of the invention.

FIG. 2B illustrates in flow diagram form an embodiment of the processflow for comparing new sensor data from a patient with historicalpatient information for the purpose of preventing or treating pressureulcers on the patient, and capable of running on the system of FIG. 2A.

FIG. 3 illustrates an accelerometer-based sensor in accordance with oneaspect of the invention.

FIG. 4 illustrates the processing of signals from a sensor as shown inFIG. 3 to determine at least orientation.

FIGS. 5A-5B illustrates the orientation of x-y-z axes relative to apatient using a sensor as shown in FIG. 3.

FIG. 6 illustrates a sample response of the x-y-z accelerometers due toa ninety degree turn, or roll, by a patient, such as turning from asupine position to lateral decubitus position.

FIG. 7 illustrates in flow diagram form the filtering steps used toisolate orientation, heart rate, breathing rate and movement data fromthe raw accelerometer signals, including feedback paths for improvingfiltering.

FIG. 8 illustrates in flow diagram form an embodiment of a filter inaccordance with this aspect of the invention.

FIG. 9 illustrates a variety of indices applied to the sensor of FIG. 3for ensuring proper location and orientation on the patient.

FIG. 10 illustrates two arrangements of electrodes for the sensor ofFIG. 3, the first comprising seven electrodes including common, and thesecond comprising three electrodes including common.

FIG. 11 illustrates an electrode orientation by which only twoelectrodes are required when spaced at a known angle.

FIG. 12 illustrates the use of sensors placed both on the patient andthe support surface that can be used to determine orientation relativeto the support surface.

FIG. 13 illustrates a visual representation of an orientation basedpressure map in three patient orientations: supine, right rotation, andleft rotation.

FIG. 14 illustrates the directions and certain orthogonal components ofthe gravitational force, normal force, and shear force experienced by apatient on an inclined support surface.

FIGS. 15A-15B illustrate the operation of a resistive sensor inaccordance with the present invention.

FIGS. 16A-16B illustrate the operation of a sensor layer such as mightbe used with resistive, capacitive, inductive or magnetic sensors inaccordance with the invention.

FIGS. 17A-17B illustrate an infrared sensor or other light sensor inaccordance with an aspect of the invention.

FIG. 18 illustrates the location of certain areas that are at increasedrisk of developing pressure ulcers and the placement of a sheet withmarkers and indicators for physical landmarks.

FIG. 19 illustrates how a system and algorithms can use a model of thehuman body and how the body moves in addition to a pressure map todetermine an estimate of the orientation and positioning of a patient.

FIG. 20 illustrates markers that can take the form of adhesive patches,top, or that are built into bandages, bottom.

FIG. 21 illustrates articles of clothing onto which markers can beattached or into which markers can be imbedded.

FIG. 22 illustrates the operation of a magnetic sensor, sensing andcausing a reaction to a marker.

FIG. 23 illustrates the operation of a support reacting to one or moremarkers, top and bottom respectively.

FIG. 24 illustrates patterns of pressure wave motion in reference to amarker.

FIG. 25 illustrates patterns of pressure wave motion as in FIG. 24 butapplied to a smaller pressure modulating surface.

FIG. 26 illustrates a matrix of horizontal pressurized rows in twonon-collinear orientations that can be pressurized or depressurized totarget pressure optimization to a particular location or coordinatewithin the matrix.

FIG. 27 illustrates a gradient of pressure change, in contrast to a moresudden pressure change, that is created in the support surface inresponse to a sensed marker, as represented by the star.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1, an embodiment of a system in accordance withan aspect of the invention is illustrated in flow diagram form. Apatient 100 requiring monitoring, and in at least some instances havingan existing wound or being at risk for developing a pressure ulcer, isassociated with one or more sensors 110. The sensors collect data aboutthe orientation, position, and movement of the patient and/or woundsand/or areas of compromised tissue perfusion and/or areas of risk. Thesensors communicate with a host system 120, typically a computer runningat least one program for processing the incoming sensor information todetermine the position or orientation or movements of a patient, woundsor areas of compromised tissue perfusion or areas of risk on thepatient. The program also uses historical and other data to analyze thesensor data and identify risks. In at least some embodiments, the data,including both the sensor data and the analytical data, is stored forfuture use.

Depending upon the embodiment, the output of the host system can providedirection to an automated care system, as shown at 130, or can displaymessages for the attention of a caregiver as shown at 140. In the latterinstance, the caregiver uses the suggestions from the system togetherwith training and judgment and makes a determination regardingmanagement of a patient's care, as shown at 150.

Referring next to FIG. 2A, an embodiment of the hardware components ofthe system of FIG. 1 can be better appreciated. More specifically, thesensors 110, a variety of which are described in greater detailhereinafter, collect patient orientation and physiologic data. In someinstances, this can include heart rate, respiratory rate, and other datain addition to patient orientation, position, and movement. The hostsystem 120 typically comprises a processing unit 125 together with atleast one data storage device. The processing unit executes one or moresoftware programs to analyze the sensor information and determine thestate of the patient, to determine care recommendations based on thecurrent state of the patient and relevant stored data, and, in someinstances directs the operation of an automated care system 130. Thedata store 135 typically comprises a hard disk, RAM, EEPROM, solid statedisk, or other memory device, and stores current and historical sensordata, health status of the patient, wound locations if any, at risklocations if any, as well as recommendations and settings for patientcare. In some systems, the data store can be integrated with or linkedto one or more of the hospital's databases, such that data in the datastore 135 is updated whenever the hospital records are updated. The hostsystem 120 communicates by either wired or wireless links with thedisplay 140 and/or one or more automated care systems 130.

Referring next to FIG. 2B, the operation of the software component ofthe system of FIG. 1 and FIG. 2A can be better appreciated. Data 200from the sensor is initially filtered and analyzed, as shown at step205, to determine if the sensor is both used and functioning properly.That determination is made at step 210; if the sensor is not functioningproperly, a notice about the deficiency is sent at step 215. However, ifthe sensor is functioning properly, the process continues at step 220,where the raw sensor data is filtered and analyzed to determine theorientation of the patient. Then, at step 225, an orientation-basedpressure map is generated, followed at step 230 by a pressure-timedetermination to assess how long areas of tissue have been subjected toa given pressure. A time input can be derived from the host 120, or aseparate time base can be used to make the pressure-time measurement.Then, at step 235, the pressure-time measurement is compared to a presetlimit, and, together with historical data, how long the area has beendepressurized, when the most recent depressurization of the areaoccurred, health conditions of patient, location of wounds, areas ofrisk, and other factors, together with historical positioning data asshown at step 240, a determination is made regarding suggestedrepositioning.

Then, at step 245, a determination is made as to whether the datasuggests that the patient should be repositioned soon. If no, theprocess ends at step 250, with, in some embodiments, the display oforientation, position, and movement data and a suggested repositioningschedule. If yes, and an automated care function exists, the decision atstep 245 results in a directive to provide automated care at step 255.Alternatively, or in the event that automated care is not successful, amessage is sent to a caregiver at step 260 advising of the need forrepositioning, as well as a suggested new position. The caregiver eitheraccepts the suggestion, indicated at 265, or provides alternate care atstep 270 based on judgment and training.

An aspect of the present invention is the sensor itself. Acceptablesensors for the system of the present invention can vary widely, andinclude sensors both in continuity with the patient's body or remote tothe patient's body. Possible sensors include accelerometers, RFIDsensing, resistive, capacitive, inductive and magnetic sensors,reflective sensors, infrared sensors, video monitoring, pressure andstress sensors, transcutaneous oxygen pressure sensors, transcutaneousCO₂ sensors, hydration sensors, pH sensors, ultrasound sensors, remoteoptical spectroscopy sensors, and laser Doppler flow sensors, amongothers.

As shown in FIG. 3, one presently preferred form of a sensor comprises amulti-axial accelerometer 305 with associated processor 310 and relatedelectronics, as shown in FIG. 3, and generally indicated by 300. Oneacceptable accelerometer is the type LIS344ALH three axis accelerometeravailable from ST Microelectronics, although sensing on three axes isnot required in all embodiments. In addition to the accelerometer, thesensor 300 can also comprise a capacitive sensor 315, a temperaturesensor 320, a moisture sensor 325, and an electrical signal sensor 330.The microprocessor 310 can comprise a built-in A/D converter and storedsensor identifier, and communicates with a base station/host 335 whichcan include a transceiver for wireless communications, located nearenough to reliably receive wired or wireless signals, through an RFtransceiver 340 and antenna 345. Alternatively, the transceiver/basestation 335 communicates with a remote host. In either case, the hostultimately links to viewing terminals 350 that can be, for example,integrated into the patient sensor or support system, in the patientroom, at the nursing station, or at other locations. It will beappreciated that, while not shown, a battery or other power source isprovided in the sensor 300. It will be appreciated by those skilled inthe art that the functions of the host can reside in several differentlocations in a system in accordance with the present invention. Forexample, the host functionality can largely reside in the sensor itself,or that functionality can coexist within the base station, or it can beexternal to both, or the functions can be split across multiple devices.

In an embodiment of the sensor, the device is stored such that batterylife is preserved until the unit is put into use. Alternatively, thesensor is designed with a rechargeable battery or other energy storagedevice such as a capacitor. A rechargeable sensor can be recharged byconnecting with a cable to some other energy source such as a powerconverter or can be recharged wirelessly through the use of an inductivecharger. A non-rechargeable system may have lower cost and be moresuitable for one-time disposable use in a hospital or other short-termcare environments while a rechargeable sensor may have greater initialcost but may be more economical in a long term-care facility, such as anursing home. The sensor can be activated by, for example, removing theadhesive backing on the unit, or by a conventional switch, or byexposure to ambient light in the patient's room, or activated uponexposure to a patient. Alternatively, the sensor can be activated bypassive RFID, which can be built into the unit itself or embedded in theadhesive backing of the unit. The sensor can also be active by RF orinductive loops. Precautions are also typically taken to protect thesensor's accelerometers. Precautions can be taken, for instance, toprevent damaging accelerative forces from acting on the accelerometer.In an embodiment, the casing of the sensor unit can be compressible soas to decrease the accelerative force of a fall or impact.Alternatively, or additionally, the accelerometer can show when anacceleration large enough to cause damage or a need for recalibration isexperienced and the sensor unit can then signal that it is damaged or inneed of calibration. In other embodiments, the sensor can also includean additional accelerometer capable of sensing accelerations greaterthan the acceptable range for a primary accelerometer, to be used tomeasure accelerations that can damage or cause a requirement forrecalibration in a more sensitive accelerometer. In an accelerometerwith more than 2 axes, all 3 axes can be used to determine orientation,providing more than one calculation of orientation that can be comparedand used as an indicator that an accelerometer is damage or in need ofrecalibration

The sensor, together with other system components as shown in, forexample, FIG. 1, can provide real-time monitoring of a patient'sorientation and surface pressure distribution over time, wherebypatients requiring intervention can easily be identified. One embodimentutilizes small, thin, inexpensive, wireless and disposable sensors thatsafely monitor the 3-dimensional orientation of a patient over time. Inone embodiment of the present invention, the sensors have an adhesivebacking, such that they can be affixed to the patient's body. In anembodiment, one or more sensors can be placed on the body at knownanatomic locations, although the anatomical location of the sensor(s) isnot required to be known in some alternative embodiments of this aspectof the invention, as explained in greater detail hereinafter. Thesensors can be placed on the body in a location that does not increasethe risk for tissue damage. In one instantiation of this embodiment, asmall sensor is affixed to the sternum or the anterior superior iliacspine (ASIS) of the patient. The sensors can also be embedded inarticles worn by the patient, such as shirts or underwear bracelets,belts, or collars, as long as the sensor does not move significantlyrelative to the patient.

The sensors used in the present embodiment can contain one or moreaccelerometers, gyroscopes, magnetometers, or other devices, which arecapable of measuring one or more conditions of the patient. Theaccelerometer can reliably and accurately measure patient tilt, patientorientation, patient movement, and vibration, and shock, as would occurwith a fall. The accelerometer can be coupled to a wireless transmittingdevice, such that there are no wires extending from the patients to whomthe sensors are attached. Wireless communication can be achieved viaradio frequency transmission. Monitoring the wireless communication fromthe body sensors enables real-time tracking of the condition of thepatient, including patient orientation and orientation-based pressuredistribution over time. Alternatively, wireless communication can beimplemented using an infrared or other optical link.

The present embodiment can be used to accurately monitor the staticangle and acceleration of patients relative to the support surface. Bycontinuously measuring the patient's orientation relative to the supportsurface the invention can determine to what extent the patient needs tobe repositioned and/or the extent to which a next-scheduled turn can beskipped or delayed. Warnings can be given in response to a predefinedcondition, such as prolonged patient position at a specific anglerelative to the support surface. The sensor data can be transferred to acentral location that manages a network of monitored patients to ensurethat all patients are being repositioned adequately. The network can beused to provide warnings to caregivers and to coordinate patientrepositioning schedules amongst caregivers.

The sensors and monitoring system described in this embodiment are ableto track the cumulative amount of time that a patient has been in aspecific orientation relative to a support surface. The system can alsoestimate the surface pressure exerted on different regions of the bodybased on the direction of the gravitational force vector (as determinedby the accelerometer), the orientation of the support surface, and theestimated magnitude of that force vector (as defined by physicalattributes of the patient, such as height, weight, BMI, massdistribution, etc.). A computer can analyze the patientorientation/surface pressure data over time for each patient, andrecommend optimal repositioning maneuvers based on this data.Furthermore, the cumulative surface pressure distribution for eachpatient can be seamlessly tracked and recorded as the patient moves toand from different support surfaces (i.e. bed, chair, wheelchair, couch,etc.). Information regarding each patient's pressure ulcer history,Braden score, and other conditions of the patient can be entered intothe monitoring system. The computer can recommend an optimalrepositioning schedule based on patient-specific data.

In one embodiment, the sensing system is properly secured to the patientin order to accurately determine the patient's orientation and surfacepressure distribution. In an embodiment, the system of the presentinvention comprises means for automatically determining if the sensorsystem is properly attached to the patient. A system that can detect andnotify the caregiver when the sensor is not attached, not attachedproperly, not oriented on the patient properly, not located on thepatient properly, or is otherwise not working properly is desirable.Such a condition, if not detected, can result in the patient being in anorientation sufficiently long to develop a pressure ulcer or experiencesome other adverse medical condition. Depending upon the embodiment, thepresent invention can use any of several methods to verify properlocation, orientation, and operation of the sensor. One set ofembodiments comprises means and method for detecting biometricparameters that indicate if the orientation sensor is properly securedto the patient. In this approach, the orientation sensor is consideredproperly attached to the patient only when detected biometric parametersfall within predefined values based on known physiological behavior. Ifthe detected biometric parameters fall outside of predefined limits,then the patient orientation sensor is considered to be improperlysecured to the patient, or not attached to the patient, and caregiverscan be alerted. The detected biometric parameters can include, but arenot limited to, skin capacitance, respiratory rate, heart rate, andtemperature. In the event of any error condition, where the measuredparameters are out of range, the system notifies the caregiver that thesystem or more specifically, the sensor or base station is not workingproperly

Another method to determine if the sensor is functioning properly is torange-check the raw data collected by the sensor. In the case of asensor that is measuring acceleration in three axes, the magnitude ofthe acceleration or the components of acceleration that exceed apredefined maximum or minimum reasonable acceleration would indicatethat the accelerometer or interface electronics are not workingproperly. In the case of other types of sensors, raw resistance, rawcapacitance, raw inductance, etc. can be range checked againstreasonable minimum and/or maximum values. The sensor can also monitorcircuit voltage levels and current levels, battery voltage and batterycurrent draw, battery charge state and report anomalous values to thebase station. The sensor can have and compare multiple time bases, forexample, more than one clock, oscillator, and/or timer. If the timebases give different values for elapsed time then the sensor can reportanomalous values to the base station. Alternatively, a sensor with asingle time base can compare elapsed time against a time base located inthe base station.

An additional method for detecting if a sensor is not working properlyis to compare the computed orientation, or location at a point in timeor a range of orientations or locations over time against what mightreasonably be expected. For example, if the computed orientation is anorientation that is impossible for the patient to assume then the sensoris likely not working properly. A paralyzed patient that is computed tosuddenly change from a supine to a prone position may indicate a problemwith the sensor. A sensor that rotates more than a prescribed maximumangular deviation, for example, 180 degrees in any plane, may indicate afailed sensor. A range of angular deviations and orientations can beidentified such that, if the sensor is found to be outside of range, anerror is indicated. Similarly, a sensor that assumes more than aprescribed maximum angular acceleration may indicate a failed sensor. Arange of orientations that is unexpected or a computed orientation thatis unexpected could also indicate that a sensor has been attached to thewrong body location. For example, a body extremity, such as the foot canassume orientations and undergo a range of orientations that isdifferent than those for the pelvis or thorax.

A properly working RF communication link between the sensor and the basestation, and between the base station and the nursing station, can beverified at a regular interval by communicating an expected messagebetween these separate system components at prescribed intervals.Failure to receive the proper message at the proper time indicates thefailure of the communication link.

Bio-metric data collected by the sensor can be used to verify its properattachment, location, and/or function. For example, even if the primarypurpose of the sensor is to collect orientation data, the sensor canalso measure pulse rate, respiratory rate, skin capacitance, opticalproperties, or other physical properties of the patient to verify thatthe sensor has been properly attached, oriented, positioned, and/or isfunctioning properly.

The sensing system described in the present invention can be used tomeasure a patient's respiratory rate. As the chest rises and fallsduring respiration, a sensor 300 placed on or near the patient's thoraxwill undergo a cyclic pattern of acceleration/deceleration. The computersystem of the present invention, including appropriate software asdescribed herein, can interpret this cyclic pattern ofacceleration/deceleration as a respiratory rate when it fits intophysiologic parameters associated with human breathing, including butnot limited to the rate, amplitude, and waveform of theaccelerations/decelerations. In an embodiment, the system can bedesigned such that it uses the respiratory rate to ensure that thesensor is properly affixed to the patient's body. If the system does notdetect a respiratory rate, it can be interpreted that the patient isapneic or the sensor may have fallen off the patient or the sensor maynot be properly attached to the patient. If the system detects anabnormal respiratory pattern (which can include abnormal breathing rateand/or abnormal magnitude of chest rise/fall during respiration), it canbe interpreted that the patient is in respiratory distress. The systemcan identify abnormal breathing patterns, such as hyperventilation,periodic respirations, sighing, air trapping, etc. If an abnormalrespiratory pattern is detected, caregivers can immediately be alertedvia an alarm mechanism.

In a similar fashion, the sensing system described in the presentinvention can be used to measure a patient's heart rate. As the heartbeats in the chest cavity, a sensitive accelerometer placed on or near apatient's thorax will undergo a cyclic pattern ofaccelerations/decelerations. A cyclic rise and fall of the chest wallthat is within physiologic limits (including, for example, amplitude,frequency, and waveform consistent with a physiologic heart rate) can bemeasured by an accelerometer 305 and can be interpreted by the system ofFIG. 1, for example, to be the patient's heart rate. The system can bedesigned such that it uses the heart rate to ensure that the sensor isproperly affixed to the patient's body. If the system does not detect aheart rate, it can be interpreted that the patient is in cardiac arrestor the sensor may have fallen off the patient or the sensor may not beproperly attached to the patient. If the system detects an abnormalheart pattern or arrhythmia (which can include abnormal heart rateand/or abnormal magnitude of chest rise/fall during a heartbeat), it canbe interpreted that the patient is in cardiac distress. The system canidentify abnormal heart patterns or arrhythmias, such as tachycardia,bradycardia, fibrillation, etc. If an abnormal heart pattern orarrhythmia is detected, caregivers can immediately be alerted via analarm mechanism. The sensor may also contain an embedded electricalactivity sensor that is capable of detecting the electrical activity ofthe heart. The sensor can also be correlated with an EKG in order toincrease the sensitivity/specificity of the monitoring system.

The patient orientation and surface pressure monitoring system describedherein can be designed to automatically feedback directly into thepressure control system of patient support surfaces. Many supportsurfaces are capable of regulating surface pressure at discretelocations. By providing the pressure control system with informationregarding the patient's position, orientation, location, movements, andsurface pressure distribution over time, the surface pressure of thesupport surface can be optimized. The surface pressure can also beregulated such that the patient is automatically rolled or repositionedto relieve pressure on any high-risk areas.

Depending upon the implementation, the sensing system described in thepresent invention can be designed for home care, nursing care, orambulatory care monitoring, without requiring direct caregiver support.The sensor can be worn by a patient (either affixed to their skin orembedded in an article of clothing) and the orientation/surface pressuredistribution of the patient can be monitored either constantly orperiodically. If the system detects the potential for pressure-inducedinjury, an audible and/or visual alarm can go off. The alarm can notifythe patient of the need to change position/orientation, and upon doingso, the alarm can automatically turn off. The alarm can be programmed toturn off only if the patient repositions themselves sufficiently. In oneembodiment, the alarm system described herein can be programmed to haveincreasing levels of audio or visual stimulation. For example, when thesystem detects that repositioning is indicated, a low-intensity soundcan be produced by the system. If the patient does not repositionthemselves, the intensity of the sound can increase until the patienthas sufficiently repositioned themselves. If the patient is unable toreposition him or herself, then caregivers can be alerted. The sensingsystem described herein can be used as a telemedicine patient monitoringsolution.

The patient orientation and surface pressure monitoring system describedherein can be used to help prevent SIDS (Sudden Infant Death Syndrome).An infant position/orientation sensor is able to detect if an infant islying facing up or face down on a support surface. Recommendations arein place for infants to sleep face up, so as to prevent accidentalasphyxiation. The sensor unit can be used to inform caregivers when aninfant, or any other person, is lying prone. The sensor can inform oralert caregivers when the infant is in a predefined orientation relativeto a support surface and can also remotely send data to caregivers, suchas via phone, pager, or computer system. The patient monitoring systemof the present invention is capable of also measuring heart rate,respiratory rate and breathing patterns by analyzing movement of thechest wall. Information regarding respiratory rate and/or breathingpattern can be displayed and/or correlated with infant or patientposition/orientation to increase the specificity of detectingpotentially harmful orientations. The patient orientation sensor can beaffixed directly to the patient's skin, or embedded in an article ofclothing, such as a diaper or pajamas. An embedded temperature sensorcan also be used to determine the skin surface temperature of the user.The sensing system can also monitor the physical location of the user,and indicate if the user has fallen, is walking, is rolling, iscrawling, etc.

The sensor 300 not only detects accelerations due to changes in apatient's position/orientation, but also accelerations due toheartbeats, breathing, other movements, etc. To improve the detection ofpatient a patient's position/orientation, it is desirable to separatesensor signals caused by changes in a patient's position/orientationfrom acceleration signals caused by other forces including breathing,heartbeats, etc. To determine a patient's position/orientation, only theacceleration due to gravity is needed. At the same time, it can beuseful in some embodiments to be able to monitor heart rate, breathing,and other vital signs with the sensor 300, as discussed in greaterdetail hereinafter. To determine patient position/orientation, it isdesirable to filter out signals due to other sources, and this can beaccomplished by the use of a low pass filter since patient turns aretypically slow compared to other movements detected by the sensor 300.An example of a cutoff frequency for the filter can be 0.1 Hz (since thelower end of normal respiratory rates is approximately 0.2 Hz), thoughother frequencies can be used. Other methods for isolating thegravitational accelerative forces include taking the average, median,mode, or some combination of these of the accelerative signal overseveral readings. These methods allow for approximately removing thehigher frequency and more random, less constant, or more cyclicalaccelerative forces. Components of the signal that give accelerationabove 1 g can also be removed as noise, since the gravitationalacceleration does not likely exceed 1 g for a user at rest. Anadditional method for isolating low frequency accelerations is toinclude an inertial mass on the accelerometer swing arm to reduce itsinherent responsiveness to high frequency movement. Such an arrangementis shown in FIG. 4, where the raw signal 400 from the accelerometer ispassed through one or more filters 405 for isolating the accelerativeforce due to gravity. Once the proper signals are isolated, thepatient's position/orientation can be determined successfully, as at410.

The method for using the sensor 300 to determine orientation can bebetter appreciated from FIGS. 5A-5B. The sensor is attached to the usersuch that the orientation of the user is measured by the accelerativeforces experienced by the accelerometer. The separate axes of themulti-axis accelerometer are often oriented orthogonally relative toeach other, and shown in FIG. 5B. Shown in FIG. 5A is a 3-axisaccelerometer with one axis (x in this case) aligned along thecephalic-caudal axis of the user, another (y) aligned along theleft-right axis, and another (z) aligned along the anterior-posterioraxis. The side-to-side rotation of the user is picked up by the z andy-oriented accelerometers. The Trendelenburg and reverse Trendelenburgtilts of the user (head to toe tilt) are picked up by the x and zoriented accelerometers. As such, it may be redundant to have more than2 orthogonal axes sensed by accelerometers. However, the redundancy canbe used for several purposes including: confirming the orientationcalculation, and using different accelerometers for different angles oforientation to allow for the accelerometers to operate in their mostaccurate angle zones.

Consider an example, where the user is tilted 30 degrees to the rightside. The component of gravitational acceleration along the x-axisaccelerometer does not change. However, it does change on the y-axis andz-axis. With the patient lying flat, the z-axis accelerometerexperiences the maximum acceleration due to gravity in thedownward/posterior direction, as it is parallel to the direction ofgravity. The y-axis accelerometer experiences minimal gravitationalacceleration as it is perpendicular to gravity. As the user tilts to theright, the component of gravity experienced by the z-axis accelerometerdecreases and the component of gravity experienced by the y-axisaccelerometer increases. When the user reaches 30 degrees of tilt to theright side, the z-axis accelerometer experiences approximatelycosine(30)g of gravitational acceleration. At this orientation, they-axis accelerometer experiences sine(30)g=0.5 g of gravitationalacceleration. For other orientations involving tilting about thex-axis/cephalic-caudal axis, the acceleration experienced by the z and yaccelerometers will follow a similar relationship where 30 is replacedby the angle of tilt. Similarly, if the user is tilted in theTrendelenburg or reverse-Trendelenburg positions, the z-axisaccelerometer experiences approx cosine(angle)g of gravitationalacceleration and the x-axis accelerometer experiences sine(30 angle)g ofgravitational acceleration. By knowing the gravitational accelerationexperienced by the accelerometers, one can then find the angle of thetilt. In the case of a simple tilt where there is only tilting about oneaxis, this can be accomplished by taking the arc-sine or arc-cosine ofthe ratio of the measured acceleration due to gravity to magnitude ofgravitational acceleration.

FIG. 6 shows sample data from a 3-axis accelerometer showing a 90 degreeturn of a user. The z-axis accelerometer initially shows a 1 gacceleration when the sensor is flat and then shows approximately 0 gwhen the sensor is at 90 degrees. Note that in FIG. 6 the accelerationis not in units relative to g but as output from the accelerometer. Theopposite is true for the y-axis accelerometer. In the case of tiltingabout more than one axis, the component of the gravitationalacceleration experienced by the accelerometers is reduced compared to anon-tilted state. For instance, if the user is in thereverse-Trendelenburg position (head tilted up relative to feet) by 5degrees, then when the user is now tilted side-to-side (i.e. about the xaxis), the z-axis accelerometer experiences cos(5 degrees)*g instead ofthe full g. As the user is tilted about the x-axis, the z-axisacceleration measurement continues to be decreased at a ratio of cos(5deg). Similarly, for the y-axis during side-to-side rotation (about thex-axis), the y-axis gravitational acceleration measured is decreased ata ratio of cos(5 deg). A similar calculation is used for any angle ofinclination of the z-axis, replacing the 5 degrees by the angle ofinclination. Similarly for a rotation about the x-axis, thegravitational acceleration measured by the z and y-axis are decreased ata ratio of cos(angle of rotation).

In general usage, if there is tilting about more than one axis, the useris tilted in the Trendelenburg or reverse-Trendelenburg position andbeing rotated about the x-axis. In this case, the x-axis accelerationcan be used to determine the angle of tilt about the y-axis usingtechniques as described above. This angle of tilt is then used in thecalculation of the rotation about the x-axis, by dividing the ratio ofthe experienced acceleration by the magnitude of gravitationalacceleration by cos(angle of tilt about y-axis) before proceeding withthe calculations to determine the angle of tilt, again as describedpreviously, e.g.:arcsin {[(measured gravitational acceleration in y-axisaccelerometer)/g]/[cos(angle of tilt about y-axis)]}=“angle of tiltabout x-axis”

The angle of tilt about the y-axis can be measured by other means aswell. The tilting about the y-axis is often related to the tilting ofthe support surface. This tilting of the support surface can bedetermined by placing or attaching a separate orientation sensor in afixed position relative to the support surface and determining theorientation of the support surface, or part of the support surface. Thiscan also be achieved by having information regarding the orientation ofthe support surface entered into the system. This data collection caneither be done manually or by directly communicating with the supportsurface (if the support surface has orientation sensors and has theability to output the data in a usable format).

In some embodiments it is desirable to calibrate the accelerometers toachieve a desired accuracy. Calibration determines constants that enableacceleration to be described in real, physical units. During“calibration”, the device's raw output can be calibrated by determiningthe appropriate constants that can be used to determine physical unitssuch as m/s/s, ft/s/s, g's, etc. The calibration process can involvedetermining the readings from the accelerometers throughout arepresentative sample of its orientations. Calibration constants can bedetermined and used to get more accurate acceleration data. One methodof determining the calibration constants is to orient the sensor suchthat it experiences 1 g and −1 g of acceleration along each of the axesin which acceleration is measured. The sensor can then be calibratedsuch that the output from the accelerometer when it experiences 1 g or−1 g of acceleration is associated with a 1 g or −1 g acceleration,respectively, This process can be done prior to distributing the sensorto end users, or it can be performed by the end user using instructionsor calibration tools that can be provided. The calibration constants canprovide, for example, multipliers and offsets such that a calibrationequation may be acceleration=(accelerometer reading)*M+O, where M is themultiplier and O is the offset. Depending on the degree of linearity ofthe accelerometer readings throughout its range, the calibrationequation can take on forms other than that of a linear equation.

Calibration of the accelerometers throughout their desired range oforientations can allow for more accurate orientation measurement. Eachtype of accelerometer, or each individual accelerometer, can be testedand calibrated depending on the level of accuracy desired. A plot of theangles calculated based on the accelerometer data vs. the actual anglebeing measured can be used to create a regression that can then be usedto improve the accuracy of the calculation. Once the regression is made,the calculation of orientation can be made using data from theregression. The physiologic heart rate has a range, speaking generously,of approximately 30 to 350 bpm. So when isolating the accelerativesignal from the heart beat, one can choose to look at signals withinthis range or a similar frequency range. A band pass filter can be usedto attenuate signals with frequencies above and below this range. Sincethe accelerative forces due to the heart beat can be large relative tothe other accelerative forces experienced in a resting user, there maynot be a need to significantly filter the data in order to detect theheart rate with reasonable accuracy. The heart rate can be detected bylooking for periodic signals that have a higher than normal amplitude ora low-pass filter can be used to attenuate signals above a certainfrequency. For example, frequencies higher than approximately 6 Hz (i.e.350 bpm) can be attenuated. It is also possible to increase or reducethe amount of filtering, by changing the attenuation or changing(shifting, narrowing, broadening, etc.) the band pass frequencies. Forinstance, for a resting patient, the range of frequencies that are mostcommon may be 35-120 bpm. A band pass filter covering this range may beuseful for most cases. It is possible to capture other frequencies byhaving a separate, wider, or shifted filter that is added on with adifferent gain or analyzed separately to accommodate for less commonheart rates. The attenuation can also be turned down to similarlyincrease the range of frequencies. A tight band pass filter (eg.covering a narrower range of frequencies or having greater attenuation,etc) can provide cleaner signals; for example, a Butterworth filter canbe used, although many other types of filters can also be used.

The quality of the filtering becomes more important when the signal issmaller or when there is more noise. Some examples of when this canoccur include: the sensor is not placed close to the heart (eg. in thepelvic area), when the user has more material intervening between thesensor and the heart or artery (eg. skin, fat, non-organic materialslike clothing, etc.), or when the pulse is weaker (eg. impaired heartcontraction or low blood pressure/pulse pressure). In such cases thefiltering becomes more important and the methods described above forimproving the filter may be required to isolate the heart rate. Theoptimal placement of the sensor is in close proximity to the heart (ormajor arteries) in order improve detection of the pulse and heart rate.Placing the sensor on the chest, especially near the sternum, is optimalfor detecting the heart rate. Placing the sensor at locations close tothe aorta or other large arteries are good sensor placements fordetecting the heart rate at locations more distant from the heart.

When the sensor is placed with the 3 axes oriented as shown in FIG. 5A,the heart rate (and breathing rate), is sensed mainly by the z-axisaccelerometer. When positioning a sensor that is intended to detectheart rate or breathing rate, the quality of the signal is improved ifat least one accelerator is positioned in approximately theanterior-posterior axis (or z-axis as shown above).

In certain cases it can be useful to keep track of when:

-   -   the heart rate (HR) is above a certain threshold    -   the HR is below a certain threshold    -   when the HR changes quickly    -   when the HR is irregular    -   when the magnitude of acceleration is above or below a certain        threshold    -   when the magnitude of acceleration changes quickly or is at a        rate above a certain threshold    -   when the heart rate detected by the accelerative sensors is        different from the heart rate detected by electrical signal        sensors.        This can be important for cases of ventricular fibrillation,        where electrical signals from the heart are present but the        mechanical heart beat is not present or is irregular. In such a        case, the accelerometer data can be compared with EKG data,        where the signal detectors for EKG data are either external or        internal to sensor 300.

Detecting the mechanical activity and/or electrical activity of theheart, as described above, can provide an indication of abnormalphysiologic conditions, such as tachycardia, bradycardia, arrhythmias,heart attacks, pulseless electrical activity (PEA), heart failure, etc.

Sensing a patient's breathing rate is also desirable in some embodimentsof the invention. The physiologic breathing rate has a range, speakinggenerously, of approximately 3 to 100 bpm. When isolating theaccelerative signals resulting from breathing, it is desirable for atleast some embodiments to choose to look at signals within this orwithin a similar frequency range. As with heart rate, a band pass filtercan be used to attenuate signals with frequencies above and below thisrange. Often the accelerative forces that result from breathing,especially with breathing at rest, are small relative to the heart rate.As such, filtering can be desirable. Methods to improve the filteringbeyond a basic band pass filter can be implemented if appropriate to theembodiment. This includes, for example, narrowing the band to between5-30 breaths per minute. A band pass filter covering this range may beuseful for most situations. Another issue is that the range forphysiologic breathing and heart rate can overlap. One can take advantageof the fact that the heart rate is usually higher than the breathingrate. The narrowed band pass filter can achieve the desireddifferentiation. The filtering can also be adaptive, such that the heartrate is detected first and then the filter adjusts so as to have anupper cutoff that is below the heart rate. As with heart rate, a tighterband pass filter can yield cleaner signals; again a Butterworth filtercan be used, among a variety of acceptable band pass filters.

In certain cases it may be useful to keep track of a patient's breathingrate, such as when:

-   -   the breathing rate (BR) is above a certain threshold    -   the BR is below a certain threshold    -   when it changes quickly    -   when it is associated with the administration of medications    -   when it is irregular    -   when the magnitude of acceleration is above or below a certain        threshold    -   when the magnitude of acceleration changes quickly or at a rate        above a certain threshold    -   when the heart rate is below the breathing rate    -   certain patterns of breathing, eg. Cheyne-Stokes respirations

Detecting the respiratory rate and breathing pattern, as describedabove, can provide an indication of abnormal physiologic conditions,such as tachypnea, hypoventilation, Cheyne-Stokes (strokes, braininjury, encephalopathy, heart failure), etc.

Patients may move on their own, and it can be useful to determine theiractivity level or lack thereof. It is important to isolate this signalfrom other physiologic signals. In general, there are components ofacceleration that are due to the normal voluntary movements of a user.These movements can have a magnitude that is greater than theacceleration due to breathing, heartbeats, and pulses. One method ofisolating a user's movement-based acceleration is to isolate theaccelerations that have magnitudes beyond those expected to be due tobreathing and heart beat/pulses. This threshold of magnitude can bepre-programmed based on physiologically normal accelerations due toheartbeats, pulses, and breathing. The threshold can also be directlymeasured from the accelerations measured on the user, either at the sametime or during another time when the patient is determined to be still.Another method of isolating movement-based accelerative signals is tosubtract the filtered signals of the heart rate and breathing from theinitial signal.

The user may be subjected to environmental noise, such as due tomachinery. Many patients that are at risk for pressure ulcers are put on“alternating-pressure” mattresses. These mattresses have a series ofindividual air columns that independently modulate their pressure,thereby creating depressurization waves that travel under the patient.Although these waves can travel very slowly, they can cause subtlemovements of the patient that will need to be accounted for. Algorithmsfor filtering out this noise, as well as any other environmental noise,will be straightforward for those skilled in the art, given theteachings herein. Environmental noise can also be due to electricalinterference, etc. Undesirable environmental noise sources may includenearby electrical or mechanical equipment, building HVAC or otherinfrastructure systems, and/or other human activity.

The movement-based accelerative sensing can be used to monitor theactivity level of the patient in order to encourage activity or todiscourage activity. It can also be used to automatically determinemobility for the purposes of charting, for example for determining someof the components of the Braden scale (i.e. mobility, activity, shearforces, etc.).

Other signal analysis can be performed on the signals from theaccelerometers. The overall waveform of acceleration due to heartbeat/pulse is known, as well as the waveform for the accelerationsinvolved in breathing. Signal analysis can be used to analyze thewaveform of accelerative signals to gain more information from thesignal, such as its source or association with different physiologicconditions. For example, the waveform for a breath is different from thewaveform for a heart beat or pulse. Thus, the waveform and/or thefrequency can be used to help isolate/identify the HR and BR. Thewaveform of a patient turn can also be identified. In addition, withinthe accelerative waveform of the heart beat/pulse, there can bedifferent physiologic conditions that affect the waveform. For instance,a different waveform exists between normal heart beats and ventricularfibrillation. Changes in waveform or abnormal waveforms can be detectedin this way. This applies similarly for breathing. The algorithms canalso learn from the normal state of the user to help better identify therange of normal HR and BR as well as the normal waveforms for aparticular user. This will be useful when any of these change greatly.This algorithm can also learn from greater data sets from one user ormultiple users to improve its accuracy and precision.

FIG. 7 illustrates the foregoing process, and shows the filters used toisolate orientation, heart rate, breathing rate, and movement data fromthe initial accelerometer signals, as well as paths to enable thefilters to learn. More specifically, in an embodiment, signals 700 fromthe accelerometers are received by a set of four parallel filters705-720, including a filter 705 for isolating gravitational accelerativeforces, a filter 710 for isolating heartbeat/pulse accelerative forces,a filter 715 for isolating breathing accelerative forces, and a filter720 for isolating accelerative forces due to movement. In addition tomovement and orientation, the acceleration measurements can be used todetect other characteristic accelerative events, such as falls. At block725, the heart rate output is used to provide an upper cutoff for thebreathing rate filter, and feeds from block 725 to filter 715. Likewise,heart rate and breathing rate can be subtracted to isolate movement, asshown by block 730 feeding to filter 720.

Referring next to FIG. 8, one of the filters of FIG. 7 can be understoodin greater detail. The accelerometer signal 800 is provided to low passfilter 805, with a cutoff below the minimum physiological breathingrate, to isolate orientation as shown at 810. To isolate heart rate, thesignal 800 is fed to a band pass filter 815 with a physiological rangeof heart rates, or a subset, as the cutoff, yielding an output of heartrate as shown at 820. In addition, heart rate data is fed via block 825to a band pass filter 830, which also receives the signal 800 andisolates breathing rate as shown at 835, including using heart rate asthe upper cut-off for breathing rate. Amplitude threshold block 840 alsoreceives the signal 800, and isolates activity and mobility level asshown at block 845.

There are instances when a patient's vital signs can be affected bypositional changes. The position/orientation sensors described hereincan be correlated with a patient's vital signs in real-time. Data fromthe position/orientation sensors can be correlated with vital signmeasurements that are obtained via standard modalities (EKG, bloodpressure cuff, manually counting palpable pulsations of the arterialpulse, manually counting respirations, etc.). Data from theposition/orientation sensors can also be correlated with vital signsusing a single sensor that can determine both the patient'sposition/orientation and vital signs. In one implementation, anaccelerometer placed on the patient can determine theposition/orientation of a patient, as well as the heart rate andrespiratory rate. When the sensing system detects dramatic changes inheart rate that are associated with changes in position/orientation,caregivers can be notified that the patient may have orthostatichypotension. Patients with orthostatic hypotension will commonlyexperience a decrease in blood pressure upon standing that is associatedwith a rapid acceleration in heart rate (usually an increase of over 20bpm). In fact, the diagnosis of many conditions (i.e. orthostatichypotension, autonomic dysfunction, postural orthostatic tachycardiasyndrome, etc.) can be aided by using a tilt-table test, where patientsare put on a platform that tilts and vital signs are monitored.

There are other instances when a patient's vital signs are affected byposition. For example, when patients with CHF lie flat they can developrespiratory distress that manifests as an increased respiratory rate.Similarly, patients with morbid obesity or obstructive sleep apnea candevelop respiratory distress when they lie flat (the extra weight due tofat around the chest and neck can increase the work of breathing) andthese patient's breathing patterns can change based on the posturalchanges. In one implementation, an accelerometer placed on the patientcan measure both the patient's position/orientation and respiratoryrate. When the sensing system detects changes in respiratory rate thatare associated with changes in position/orientation, caregivers can benotified and further workup initiated.

Conditions that can be affected by position can be entered into themonitoring system. For example, if a particular patient has CHFresulting in severe orthopnea, this condition is entered into the systemand then the turning recommendations allow for the patient's head/chestto remain elevated by 30 degrees throughout the day (patient's with CHFcan't handle the extra fluid load that occurs when lying supine, hencethey get short of breath when lying flat). As a consequence, since thepatient's head/chest is elevated throughout the day (thereby increasingthe pressure-dose on the sacrum), the system can then recommendincreasing turning frequencies, etc. to help prevent sacral ulceration.Any condition of the patient (i.e. paralysis, amputations, injuries,diabetes, anorexia, obesity, etc.) can be defined in the system.

It has previously been described herein how sensing the patient'sbreathing pattern and heart rate can be used to determine if the sensoris properly affixed to the patient.

Similarly, electrodes or capacitive sensors which are capable ofmeasuring the body's electrical activity, impedance, or resistance canbe used to determine if the sensor is properly affixed to a patient. Athermometer can also be used to determine if the sensor is properlysecured to the patient. When the skin surface temperature reading showstemperatures sufficiently close to the expected skin temperatures, itcan be assumed that the sensor is affixed to the patient. Similarly, ifa sudden change in the skin surface temperature is detected, it can beinferred that the sensor has lost continuity with the patient.

Another technique that can be used to determine if the sensor unit isproperly attached to the patient is a tab that is attached to aconductor within the sensing unit's circuitry. After the unit is affixedto the patient, if the unit is subsequently removed, the tab detachesand changes the circuit in a measurable way, such as by changing theresistance. This allows the sensing unit to know that it has beenremoved from the patient and the sensing unit can send this informationto the host or other reader. In some arrangements, the tab can also beaffixed with greater strength to the patient due to differences inaffixing compound or a heat-activated bonding substance.

The sensor unit can be oriented to work automatically when placedanywhere on the patient. In this care, orient means to determine thedirection of the accelerometer with respect to gravity or with respectto the patient. During “orientation”, the accelerometer's direction canbe determined with respect to gravity by measuring the acceleration inthe three axes as the device is rotated in each of the three axis ofrotation. Some placements can be at the sternal notch or the xiphoidprocess of the sternum or the anterior superior iliac spine (ASIS). Thesensor unit can also be placed anywhere on the patient and oriented tothe patient. In an embodiment using this approach, the patient liessupine with the sensor unit in place. A button on the reader unit, thesensor itself, a remote, or a computer interface can be pushed or acommand sent once the patient is supine, and the reader unit will thenassociate the reading from the sensor unit with the supine position.Thus, the sensor unit can be at placed at any angle relative to thepatient and the system will be able to oriented accordingly. The signalto the system that the patient is supine can come in any number of formsincluding voice activation, etc.

Different sensors can be pre-calibrated for use on patients withdifferent body types. For example, a sensor that has a unique identifiercan be placed on patients that have a specific BMI. In such a manner,the system will detect the unique identifier from the sensor, andautomatically calibrate the monitoring system for a patient with aspecific BMI.

Similarly, the sensors placed on the support surface can bepre-calibrated for use on support surfaces with different properties.For example, a sensor that has a unique identifier can be placed onsupport surfaces that have a specific surface pressure profile (i.e. drypressure, air pressure, air fluidized, etc). In such a manner, thesystem will detect the unique identifier from the sensor, andautomatically calibrate the monitoring system for a support surface witha specific surface pressure profile.

In at least some embodiments, the sensing system is designed such thatit does not require any additional manipulation by a care provider. Aspreviously described, the sensor can automatically be activated when itsadhesive backing is removed. The removal of the adhesive backing allowsfor the activation of a sensor circuit and hence discharge of the unit'son-board battery. To conserve power, the sensor can locally storeacceleration data and transmit this information to the receivingstation(s) at predefined intervals. A disposable sensor unit can bedesigned such that it is able to transmit acceleration data for anextended period of time, such as days or weeks.

The sensor unit can be designed such that it does not draw power (or atleast very little power) when it is in its packaging. In someembodiments, it is activated immediately before being placed on thepatient. Alternatively, a signal received from the transceiver can serveto activate the sensor unit. One type of activation signal can be an RFsignal that is sent to the unit. If the sensor unit is not a passive RFunit, the unit can temporarily act as a passive tag before activationand be powered by the received signal. As another alternative, a passivetag or an RF receiver/transceiver that has the ability to passivelyreceive signals can be initially included as part of the sensor, and canbe used to allow for a signal to be received by the by the sensorwithout using stored energy in the sensor. This signal can be used toactivate the sensor. The passive tag can then be removed promptlyfollowing activation, as a method for reducing the size of the sensingunit and allowing the passive receiver/transceiver antenna to be larger.

For units that sense physiologic variables such respiratory rate, heartrate, and/or temperature, in an embodiment the reader can allow for aperiod of time (seconds, minutes, or hours) after activation before itexpects physiologic values to be measured. This can allow time to attachthe sensor to the patient before the system expects to receivephysiologic data.

Another variation has the sensor activated by a switch on the unit.

Proper placement of the sensor 300 on the patient is important in atleast some embodiments. In at least some embodiments, the sensor isplaced on the patient such that there is no potential for movement ofthe sensor with respect to the patient. In an embodiment, the sensor isadhered directly to the skin using an adhesive patch, which can besimilar to that used for standard EKG leads, although in other instancesthe sensor can be removed from the adhesive backing to permitreplacement of the sensor while protecting the patient's skin.

The sensor is ideally placed on the anterior thorax, pelvis, upper thighor shoulder. In ideal usage there is little relative movement betweenthe sensor and the user's pelvis, which enables an approximatedetermination of the orientation of the user's pelvis. In an embodiment,the sensor must be placed at a location on the body where theorientation of the sensor approximates the orientation of the patient'spelvis and/or thorax.

By knowing the orientation of the patient's pelvis and/or thorax, thesurface pressure distribution across other body structures can beestimated. For example, if it is determined that a patient is in acompletely supine orientation, it is then known that surface pressure isbeing exerted on the patient's sacrum, and ischium. However, based onthe patient's orientation and the known anatomic relationships thatexist between different body structures, it can be inferred thatstructures such as the posterior occiput, elbows and heels are alsoexperiencing pressure. If the patient then turns to a left lateraldecubitus position, it can be determined that surface pressure has beentransferred to the patient's left hip, as well as other body structures,such as the left shoulder, left elbow, left occiput, and left lateralmalleous.

When the patient's pelvis is determined to be in a left lateraldecubitus position, it is very unlikely (if not impossible) for surfacepressure to be exerted on the patient's right hip, right occiput, rightelbow, right shoulder, or right lateral malleolous. There are anatomicrelationships that exist between different body parts that preventpressure from being exerted at these locations. In such a fashion, theoverall surface pressure distribution map of a patient can be estimatedbased on the known orientation of one or more body structures, such asthe pelvis or thorax.

In at least some embodiments, it is preferred that the sensor not beplaced on the limbs or head, because the orientation of the limbs doesnot always approximate the orientation of the pelvis/thorax. Thelocation of placement may be different if the primary concern is forpreventing and managing pressure ulcers at locations other than thepelvic region. For example, if the patient has a pressure ulcer on theirright heel, a sensor can be placed on or near the right foot, ankle, orlower leg to better approximate and monitor the orientation and surfacepressure distribution of the affected region. In an embodiment, thesensor should not be placed in a location where it will be susceptibleto being rolled on.

In order to accurately determine a user's orientation, it is importantin at least some embodiments to know the orientation of the sensor withrespect to the patient. To facilitate properly orientating the sensorwith respect to the patient without requiring significant training, anindex mark can be provided on the sensor 300. Such index marks canprovide information including but not limited to which direction thesensor should be oriented (eg, top of sensor towards the patient's head)or where on the patient the sensor should be placed. Examples of indexmarks are shown on the different sensors 900A-900E illustrated in FIG.9, including two, 900C-D, with cross-hairs on a representation of ahuman for indicating the location where the sensor should be placed andwhere the orientation of the human image on the sensor is to be alignedwith the user (i.e., head pointing in same direction in image and user).The three other examples in FIG. 9 are for indicating simply the desiredorientation of the sensor including an arrow, an arrow labeled “head”,and a human image representation. In an embodiment, the orientation ofthe sensor with respect to the patient must be determined to accuratelydetermine the relative surface pressure distribution of the patient. Theindicia need not reference the head, as long as there are sufficient andsimple instructions or indicia to place the sensor relative to anidentifiable landmark on the body and a in a relative orientation tothat landmark, whether the landmark be the sternum, belly button,anterior superior iliac spine (ASIS) spine, leg or other. The indiciacan include but are not limited to markings on the sensor, the shape ofthe sensor itself, different materials or colors used on different partsof the sensor, or asymmetry of the sensor. The shape of the sensor oradhesive backing can also be more suitable to fitting in or conformingto specific areas of the body in specific orientations. The sensor canbe incorporated into articles that may be worn by the patient such thatwhen the article is worn the sensor is in an appropriate location andorientation.

In an embodiment, it is possible to automatically determine theorientation of the sensor 300 by, for example, sensing bioelectricalsignals in the body. It is well understood that electrical impulsespropagate away from the heart in a well-defined pattern, and the bodyhas a known and well-defined polarity that can be detected. Referringnext to FIG. 10, by providing the sensor 1000 with multiplebioelectrical sensors 1005 positioned circumferentially around the outersurface of the sensor, the plurality of bioelectrical sensors can beused to detect the average direction of electrical propagation, andeither the sensor itself or the remote host can process the data toidentify the orientation of the sensor 1000 with respect to the heart.In such an arrangement, the sensor 1000 can be placed on the patient atvirtually any location on the thorax/pelvis (and in any orientation) andthe sensor can automatically determine its orientation with respect tothe patient.

Referring still to FIG. 10, the sensor picks up the electrical signalbetween the electrodes shown as open circles in reference to the commonelectrode 1010 shown as a solid circle and depending on the vector ofthe body's electrical signal at the location of the sensor can determineits orientation with respect to the patient. The magnitude of the signal(which can be an average or integrated magnitude) from the differentelectrodes gives an indication of the direction of the vector. Forinstance, if the signal from one of the electrodes shows a greatermagnitude than the rest, then the vector can be determined to be closestto the direction of the line intersecting that electrode and the commonelectrode. The vector can also be determined to be in the directionbetween the two electrodes with the greatest magnitude of detectedsignals. As the signal detected in the electrodes can be positive ornegative, the plurality of electrodes need only span approximately 180degrees, for example, roughly a semicircle, to determine the vectordirection within a 360 degree range, thereby reducing the number ofelectrodes needed per device and the number of sensing inputs and/or A/Dconverter inputs.

An alternate method for reducing the number of electrodes is to use twoelectrode sensing vectors spaced at a known angle (90 degrees is oneexemplary implementation) as shown in FIG. 11. Based on the magnitude ofthe detected bioelectrical signals in each, the vector direction can bedetermined. This is illustrated in FIG. 10 where sensor 1015 compriseswith electrodes 1020 and common electrode 1025.

Alternatively, using the sensor's built-in accelerometer, normalphysiologic movements of the body due to respiratory and cardiacactivity can be detected. The heart and lungs produce movements of thethorax, and these movements have a characteristic trajectory. Byanalyzing the trajectory of motion of the thorax due to cardiac andrespiratory activity, it is possible to know the orientation of thesensing unit with respect to the patient.

As a still different alternative for self- or auto-calibration, thesystem can identify any accelerations that fall outside of the range ofwhat is known and expected from normal movements of the human body. Ifthe accelerometer is not placed correctly on the patient, when thepatient is rotated it will appear that they are moving in a manner thatis not compatible with normal body movements. If this is the case,caregivers can be alerted to confirm that the sensor is properly placedon the patient. Alternatively, the system can automatically re-calibrateitself to some extent by knowing the range of possible patient movementsand correlating this information with data from the sensor. Caregiverscan also provide input to the system regarding which direction theyturned the patient and a learning-algorithm can then be used tocalibrate the orientation sensor.

Since the system will coordinate patient turning, and may be used todocument compliance with turning protocols, it is important in at leastsome embodiments to be able to confirm that the sensor is properlyaffixed to the patient. The sensor can detect specific physiologicparameters when it is properly placed. Sudden loss of signal ofphysiologic parameters indicates that the sensor is no longer properlyplaced on the patient, or the patient is having an acute event. Forexample, in one embodiment, the sensor can detect the capacitance of theskin. If the detected capacitance suddenly changes, it can be determinedthat the sensor has lost continuity with patient. If it is determinedthat the sensor has been removed from the patient, the sensor can belocked out and rendered nonfunctional, thereby avoiding any risk ofaccidental or fraudulent manipulation of the sensor.

In addition, each sensor can be assigned a unique identifier, and, in anembodiment, can be linked to a particular patient, for example either bya scan or other electronic data entry. Aside from avoiding erroneousreadings, this permits a single monitoring system, such as shown in FIG.1, to monitor a plurality of sensors.

In many cases it is important that the sensor data is associated with acertain patient. This may be the case in care settings in which there ismore than one patient. It may also be the case in single patientsettings in which the data from the patient needs to be stored andidentified or associated with the patient. The needs of different caresettings vary in terms of how they want the data from the system to bemarried to the patient/user. In one potential usage scenario, the carefacility wants the patient data to be married to a sufficiently uniquepatient identifier, such as a medical record number (MRN). Otheridentifiers can include name, date of birth, room number/bed number,etc.

Where the care facility would like to associate the data with an MRN,there are several ways that the association can be made. In one method,a user may enter the MRN into the system of the present invention. Thesystem can then send data along with the MRN or can be polled for theMRN associated with the data as needed.

The system can also assign a unique identifier to the data from a givensensor or group of sensors. This unique identifier can be different fromthe unique identifier of the patient used by the care facility. Theunique identifier can also be a sufficiently unique identifierassociated with the sensor itself that is used by the system todistinguish which sensor the received data is coming from. The carefacility can then associate the unique identifier from the system withtheir identifier of the patient separately, in a separate computersystem for instance.

One method for easily associating the MRN with the sensor can be thatthe user/caregiver scans the MRN from a scannable identifying unit onthe patient (eg, bracelet with barcode, or RFID) or from some othersource: eg chart, sticker, bed, etc. The sensor can also be scanned orpolled for its identifier and the patient identifier and sensoridentifiers can be married automatically at the bed side with thepatient to reduce the likelihood of error. In an embodiment, thescanning system forms part of the present invention, and can becomprised of, but not limited to, an RF reader, a barcode reader, or avisual text recognition system. The sensor itself may include a scannerfor the patient identifier and can then transmit that information to thehost system.

During the marriage process, the system will need to know which sensoror sensors are being married to the patient identifier. Thecommunication range of the sensors may mean that sensors other than thedesired sensor(s) are within range. One method to associate the correctsensor is to have a short range RF reader to read the specific sensorbeing used. The user/caregiver may use a handheld short range reader toscan in the correct sensors. The short range reader may also be on abase station reader within the room. The user/caregiver can hold thedesired sensor(s) in close proximity to this short range reader whenperforming the marriage of the sensor and patient identifiers. The shortrange reader may also be the same reader as the reader for receivingsensor data, but placed in a short range read mode, which may beachieved by reducing the power of the reader's transmission orincreasing the threshold of received signal power for the receivedcommunications. The user/caregiver may activate the short range readingmode of the reader with a button or by other means. The marriage mayalso occur when the sensor is activated.

In one example of use, the caregiver first scans the patient's braceletwith a handheld scanner which includes the barcode scanner. The uniqueidentifier of the patient is read into the system. The system thenprompts for a sensor to be scanned. The caregiver scans one or moresensors with the handheld scanner which also includes a short range RFreader. The system then marries the identifiers for the patient andsensor.

The same methods above can be used for identifiers other than the MRNsuch as the name, date of birth, room, bed, etc.

In the case of the room or bed, the base station may be able todetermine from signal strength or its read range what bed or room thesensor is in. For example, a base station may have sufficient read rangeonly to receive data from sensors within a room or from a specific bed.Directionality of the base station reader may also be used to determinethe location of a sensor. This directionality can be achieved with anantenna with greater directionality. One or more antennas can be used ina setting where there will be one or more patients per base station. Asingle antenna can vary its direction between communications. Theuser/caregiver can change the direction the antenna is pointing or thedirection of its maximal gain on the base unit, where an indicator canshow the antenna's direction. The system can then associate the bed orroom number with data from a sensor or group of sensors. This marriageof sensor(s) to a specific room or bed may be sufficient for a givencare facility to determine which patient is being monitor by whichsensor(s).

The monitoring system of the present invention can track, record, anddisplay relative surface pressure distribution data for a patient andalert caregivers when it's indicated to reposition a patient. Since theorientation sensor is placed in a known orientation relative to thepatient (using visual indices and auto-orientation mechanisms), thesystem has the ability to know when pressure is being exerted onspecific areas of their body. The system can also determine thecumulative amount of time that pressure has been exerted on specificareas of the body, and thereby calculate the pressure dose for specificareas of the body. The system can monitor the pressure dose at specificareas of a patient's body, and use this information to determine apatient's requirement for repositioning. The system can use thisinformation to help ensure that patients are turned as often asnecessary, but not more often than necessary. In addition, the systemcan suggest the optimal direction to reposition a patient by analyzingthe pressure dose at specific areas of the patient's body and suggestingrepositioning maneuvers that allow for the patient to be preferentiallypositioned onto regions of the body that have a low pressure dose.

Still further, the system that can automatically detect when a patientinitiates a turn by themselves or if a turn is initiated by acare-giver. In an embodiment of this aspect, an RFID tag on thecaregiver's badge configured to be recognized by the orientation sensoron the patient or by the base station residing near the patient. Whenthe two (ID badge and patient sensor) come in close proximity with eachother, and the system subsequently detects a patient turn, it can benoted that the turn was performed when a caregiver was present. Othermethods for doing this include having a button on the sensor or userinterface that is pressed to indicate a care-giver turn was performed;still others will be apparent to those skilled in the art, given theteachings herein. This information can be helpful, as it may be a factorthat helps indicate when a patient is sufficiently mobile, and thus nolonger requires continued monitoring and caregiver assistance. However,if a patient is determined to not be moving sufficiently on their own,it may indicate that this patient requires continued monitoring andcaregiver assistance.

In another aspect of the present invention, the system not only keepstrack of how long a user has been exerting pressure on specific areas oftheir body, but also keeps track of how much time specific areas of thebody have had to depressurize. This is important because sufficientblood flow to a tissue (where it is free of pressure above a thresholdthat restricts blood flow), is required for a sufficiently long periodof time in order to resupply said tissue with oxygen and vitalnutrients. This is referred to as the re-perfusion interval. The desiredre-perfusion interval can be set by the user, by caregivers, or can betaken from a protocol. The re-perfusion interval may also vary dependingon the patient. For example, a patient's co-morbidities, Braden score,nutrition status, past history of pressure sores, or feedback fromperfusion sensors can be used to determine an appropriate re-perfusioninterval.

Knowing the patient's orientation relative to the support surface can beimportant for pressure ulcer management. When information regarding boththe orientation of the support surface relative to gravity and theorientation of the patient relative to gravity is provided, the systemcan determine the relative normal force of the support surface(pressure) as well as the tangential force of the support surface (shearforce).

Orientation/inclination sensors 1200 can be placed on the supportsurface to directly measure the orientation of the support surface asshown in FIG. 12. These can be placed, for instance, on the mattress,the bed frame, etc. These sensors can be the same or different from thesensors 1205 that are placed on the patient. These sensors cancommunicate with the same or different wired or wireless transceivers.By using different sensors for the support surface and the patient, orby using sensors with different unique identifiers, the system caneasily distinguish between information sent from the support surfacesensors and information sent from patient sensors. One or more supportsurface sensors can be placed on or they can be contained within thesupport surface. With one sensor, tilting of the support surface as aunit (eg. right, left, Trendelenburg, etc) can be measured. With morethan one sensor, the orientations of different parts of the supportsurface can be determined, such as with tilting of the head of the bed.

Support surfaces can have embedded sensors that are used for determiningits orientation and positioning. Data from these sensors can be used toprovide our system with information regarding the orientation of thesupport surface. In such an embodiment, the host communicates with thecomponents of the support surface, for example, embedded theprocessor(s) r or sensor(s), to gather this data.

Support surfaces have several common orientations and configurations.These include flat, head up, Trendelenburg position, reverseTrendelenburg position, rotated right, rotated left, combinations ofthese, etc. The orientation data for these common and possible supportsurface positions can be programmed into the system so that theorientation data does not have to be measured directly. A user canselect which orientation the support system is in (including specificangles in some embodiments) and the system can use that data todetermine the orientation of the patient relative to the supportsurface.

If information regarding the orientation of the support surface is notprovided to the system, it can be interpreted that the support system isin a default orientation, such as horizontal to gravity.

Knowing the orientation of the patient relative to the support surface,and the orientation of the support surface relative to gravity, allowsthe system to generate an estimate of where on a patient's body surfacepressure is being exerted, and an orientation-based surface pressuredistribution map can be generated. This data may also be used toestimate the magnitude of the pressure per unit weight of the patient.Information regarding the weight and mass distribution of a patient canbe used to estimate the absolute pressures being experienced atdifferent regions of patient's body.

At different angles of patient rotation relative to the support surfaceand to gravity, the patient experiences pressure on different portionsof their body. This is the basis for the turning protocols, which allowsfor periodic depressurization of areas of the body in sequence. Thesystem can determine, from the orientation of the patient relative tothe support surface and to gravity, which areas of the body areexperiencing pressure, and thereby creates an orientation-based pressuredistribution model of the patient. A representation of theorientation-based pressure map is shown in FIG. 13. The system can alsokeep track of how long the patient is in any given position and thus howlong certain areas of the body are experiencing significant pressure. Asthe patient is repositioned, the system can monitor the angle of patientrotation, and determine if there was a sufficient change in a patient'sorientation, so as to provide a threshold level of depressurization atspecific areas of the patient's body. For example, if the patient isinsufficiently rotated, certain areas of the body may not experiencedepressurization. The system can monitor and track the pressure atdifferent body regions using the orientation-based pressure distributionmodel. The system can determine when certain body regions requiredepressurization, and thus indicate that a change in patient orientationis required. In such a fashion, the system can optimize a patientturning schedule and ensure that patients are turned as often asnecessary, but not more often than necessary. The system can also ensurethat patients are turned with sufficient frequency and with sufficientde-pressurization intervals so as to provide sufficient time for tissueperfusion.

The orientation-based surface pressure distribution model determines thesurface pressure distribution as a function of the patient's orientationrelative to a support surface. When the patient is supine, surfacepressure is distributed over the back of the patient. When the patientrotates onto their side, surface pressure is distributed along thecorresponding side as a function of the angle of patient rotation.

An orientation-based relative surface pressure distribution model can begeneralized without taking into account actual or absolute pressureestimates. However, the present invention can also incorporate apatient's weight, mass distribution, BMI, and other characteristics inorder to estimate an orientation-based absolute surface pressuredistribution model. Certain patients and/or caregivers may choose tocalibrate orientation-based pressure distributions by going through acalibration procedure that can involve rotating at different angles andviewing pressure distribution using a pressure measurement device, suchas a pressure mat.

Knowing the orientation of the patient relative to the support surfaceand the orientation of the support surface relative to gravity allowsthe system to estimate the shear forces acting on the patient, inaddition to the normal force pressure. Shear force acts on the patientwhen the support surface is angled and there are forces actingtangential to the patient's skin. These shear forces contribute totissue damage and minimizing shear force is important for pressure ulcermanagement and skin health.

One method for estimating the shear force on a patient comprisesdetermining the orientation of the patient relative to gravity anddetermining the orientation of the support surface relative to gravity.A processing device and corresponding algorithms then determine theorientation of the patient relative to the support surface. When thepatient is static, the gravitational force acting on the patient iscountered by the component of the normal force of the support surfacethat is in the opposite direction of the gravitational force vector andcountered also by the component of the shear force that is in theopposite direction of the gravitational force vector. The directions ofgravitational, normal, and shear forces are illustrated in FIG. 14, aswell as their components parallel and orthogonal to the direction of thegravitational force, where the below relationships can be seen:Gravitational force−Vertical component of normal force=Verticalcomponent of shear forceShear force=Vertical component of shear force/sin(Angle of Inclinationof support surface)

Thus, the angle of the support surface gives a measure by which we candetermine the relative magnitude of shear forces acting on the patient.Knowing patient specific data, such as the weight of the patient, canallow an estimation of the absolute magnitude of the shear force.

The estimate of the shear force can be combined with theorientation-based pressure map and the support surface orientation datato provide an estimate of where the shear force is acting. The tissueareas that are receiving pressure are also areas that may be subjectedto more shear force. The magnitudes of pressure and shear force for anygiven area of tissue can be correlated. This information can be used tocreate an orientation based shear force map. The system can use thisdata to adjust its repositioning recommendation in order to minimizeshear force damage. For instance, the amount of time a given areareceives shear force or a magnitude of shear force experienced can bemeasures that the system attempts to minimize or limit.

The single sensor or sensors positioned only on the patient can be usedto determine the orientation of the patient relative to the supportsurface and to gravity. For example, any sustained inclination in thex-z plane as defined in FIG. 5A can be interpreted as an inclination ofthe bed. Through an analysis of the orientation with respect to gravity,over time, of a single sensor placed on a patient, support structureorientation can be determined for structures having more flexibleconfigurability.

The present invention also permits automation of various parameterstypically used to calculate a patient's Braden score. At present, someof these parameters are taken subjectively. However, the presentinvention permits some of these parameters to be determined much moreobjectively, and with automated data entry into the patient chart, themonitoring system, the support surface, or any associated data storageunit. The parameters that are assessed subjectively by the prior art,but which can be objectively assessed using the monitoring systemdescribed herein, include the patient's mobility level, activity level,moisture level, and any friction and shear forces experienced by thepatient. The mobility and activity level can be measured by the sensorunit as described above. With the addition of a moisture sensor, theunit can also provide an objective assessment of the skin moisturelevel. The acceleration of the patient relative to the support surface,as described above, can also be analyzed to determine the magnitude ofany friction and shear forces experienced by the patient. The ability ofthe patient to move without sliding can be determined by theaccelerations experienced by the accelerometer. Integrated accelerationsto determine cumulative distances moved, and the addition of gyroscopesand/or magnetometers can help determine friction/shear forcesexperienced by a patient. While the two remaining variables thatcomprise the Braden score, (i.e. nutrition status and sensoryperception) can not be measured by the monitoring system describedherein, these variables are much less likely to change frequently andthey can more or less be considered constant. Thus, once informationregarding the patient's nutrition status and sensory perception areprovided to the system, the system can thereinafter automatically andobjectively determine a patient's Braden score in real-time.

With the improved monitoring of patient repositioning and surfacepressure distribution data, it is possible to better assess theeffectiveness of a turning protocol. Whereas many current protocolssuggest turning every two hours, this may not be the best protocol forall patients. For example, certain patients with existing wounds, poornutrition, poor wound healing, etc, may require more frequent turning.Certain patients, with better health and fewer wounds may require lessturning, allowing for better rest and reduced caretaker involvement.Improved monitoring can be invaluable for facilities who want to assessthe effectiveness of the turning protocol. The present invention canalso include features which allow for active data collection toautomatically suggest variations in the turning protocol. In anembodiment, the system can use data about the patient, such as theBraden score or components that affect the Braden score of a givenpatient. Other useful data includes the presence of wounds, pressureulcers, history of pressure ulcers, etc. Data about pressure ulcerdevelopment and progress, such as healing or worsening, can also beentered. Depending upon the embodiment, the present invention can adjustthe suggested turning regimen based on how well a patient is doing onthe current regimen or how well the patient has done in the past on aturning regimen. The invention can also allow for minor adjustments inthe turning regimen and use data about the progress to determine whichregimens are better. Changes in regimen can include, but are not limitedto, frequency of turns, time spent in a given position, time thatcertain areas of tissue spend in depressurized states, orientationangle, amount of pressure and time spend on wounded or previouslywounded areas, etc. In some embodiments, additional sensors and data canbe used to assess the progress, including perfusion sensors, area anddepth measure of the wound, stage of wound, etc. Data can be collectedfrom more than one patient, for example patients within a facility orward or in fact all patient to help assess the performance of anddetermine potential improvements for care protocols.

A pre-existing pressure ulcer or other wound, may be more easily damagedby pressure and shear forces. Part of the treatment for that ulcer orwound may be to reduce the maximum pressure experienced by the damagedtissue and surrounding tissue and/or to reduce the amount of time thatpressure is exerted on the tissue. Similarly, the treatment may includelimiting the amount of shear force experienced by the tissue.

In another aspect of the present invention, the locations of existingpressure ulcers, wounds, and other pressure-sensitive areas of the bodycan be identified and entered into the monitoring system. The thresholdamount of time that pressure can be exerted on the pressure-sensitiveregion can be adjusted, as well as the depressurization intervaldesired. In some instances, it is desirable to have no pressure on anarea of damaged tissue, since the pressure appropriate for wounds suchas pressure ulcers, incisions, skin flaps, etc., is much less than thatfor healthy tissue. In such a scenario, if it is determined thatpressure is being exerted on an area of damaged tissue, the system canset off an alarm to inform the patient and/or caregiver(s) to adjust theposition so as to depressurize the wound area. In addition to wounds,the system can also be configured to permit entry of any other areasthat require surface pressure monitoring. These areas can includeshoulders, hips, feet, etc. The user/caregiver can enter the location inmany ways, some examples including: a pull-down menu of wound sites, atext entry, a graphical interface with a graphical representation of thepatient in 2D or 3D, etc. These are described in more detail below. Inaddition, different sensors can be pre-programmed for use at specificbody regions. The pre-programmed sensors can contain information aboutthe location at which they are meant to be placed and/or containspecific pressure thresholds, depressurization interval thresholds, orother care data.

The user or caregiver can manually enter the locations of the wounds.One method of entry is to show a 2D (from one or more views, egposterior, anterior, L lateral, R lateral) or 3D model of the patient(or a generalized patient, perhaps chosen from a list to closely matchthe patient) and have the user select the locations where the pressureulcers or other wounds are present on the model. This model can berepresented on a computer display with a mouse or touchscreeninteraction to allow for location selection. Selections on a 2D modelcan be mapped to a 3D model of the patient.

Another method includes choosing from common or possible locations forpressure ulcers, such as: ischial tuberosity, trochanteric, sacral,malleolar, heel, patellar, pretibial, nose, chin, forehead, occiput,chest, back, and elbow locations. If the location of the wound fallsoutside of the list and no entry approximate sufficiently the location,then the user may enter locations relative to the entries, eg 2 cm @ 3o'clock direction from patellar location.

The user may choose from one or more entry methods depending on what ismore appropriate and efficient. The user can also enter details aboutthe pressure ulcer including stage, size, shape, depth, age, skin caredetails, etc. Depending upon the embodiment, the system can alsoself-populate data on wound and ulcer locations based on the chart,which can be later adjusted by the user. In other embodiments, sensiblemarkers can be placed on the patient to designate the location of thewounds or ulcers.

Using the location of the wounds and ulcers, the treatment can bepersonalized. In an automated treatment/prevention bed, for instance,pressure can be reduced at the location of the wounds and differentpressure varying modes can be used. For recommendations of repositioningregimens, the recommendations can reduce the amount of time the patientmay spend on locations of wounds or ulcers. If positing on an existingwound or ulcer in unavoidable, embodiments of the present invention cantake into account the relative severity or risk of deterioration of thedifferent ulcers, which can, for example, be entered by the user, todetermine which ulcers/wounds it preferentially avoids.

Several features can exist in the present embodiment that make thesensor less expensive to manufacture and thus more amenable to beingdisposable. One such feature is that only the electronics and circuitryneeded to fulfill the duties of the sensor can be included in thedesign. In one simplified embodiment, the main components can includeonly an accelerometer, A/D converter, microprocessor, RF transceiver,and antenna, with many of the desired features, including basicphysiological signal monitoring, covered by the these components. Insome embodiments, a 3-axis accelerometer can be replaced by a 2-axisaccelerometer. The microprocessor need not be powerful in allembodiments, where much of the computation is configured to take placeon the host system. Also, one or more components can be included on asingle chip, for example a chip with a microprocessor, A/D converter,and RF transceiver, or a chip with all of these plus the accelerometer.Such an embodiment can significantly reduce the cost and/or size of thesensor. Again depending upon the embodiment, the battery, or otherenergy storage unit like a capacitor, can be disposable rather thanrechargeable. This can reduce the size and cost of the energy storageunit. The sensor battery can also be designed to operate until it isgreatly discharged, which allows for a greater amount of usable energyfor the same energy capacity storage but is less amenable to arechargeable unit. As well, with a non-rechargeable unit, theelectronics and circuitry needed for recharging, including leads or aninductive loop or antenna, can be left out of the sensor.

The system can be used to monitor patients that are receiving vibrationor percussion therapy. Often, patients with lung disease will requireregular vibration/percussion therapy to help clear mucus and secretionsfrom their airways. The sensors described herein can detect vibration ofthe chest wall. The monitoring system can be used to quantify themagnitude of vibration/percussion therapy, the session length of time,and the frequency of sessions. The monitoring system can be used to helpcoordinate vibration/percussion therapy for patients. If a patient isnot receiving adequate vibration/percussion therapy, caregivers can bealerted via an alarm mechanism. The monitoring system of the presentinvention can also provide feedback to devices used for automated meansof vibration/percussion therapy. The force of vibration/percussiontherapy produced by an automated source (such as a bed) can be regulatedbased on data from the sensor placed on the patient in accordance withthe present invention.

The sensing system described in the present invention can be used tomonitor patients that have been prescribed an incentive spirometer. Manyhospitalized patients are encouraged to use an incentive spirometer tohelp prevent atelectasis and improve lung function. As previouslydiscussed, the sensors described herein can detect acceleration of thechest wall. The monitoring system can be used to quantify the magnitudeof incentive spirometry therapy, the session length of time, and thefrequency of sessions. Statistics regarding a patient's incentivespirometer usage can be provided to both the patient and caregivers. Ifa patient is not receiving adequate incentive spirometry therapy,caregivers can be alerted via an alarm mechanism. The sensing systemdescribed herein can be used to assess compliance with, and adequacy of,prescribed incentive spirometry regimens.

In an embodiment, the monitoring system comprises a sensor affixed to apatient whereby the sensor data is wirelessly transmitted to one or moresignal receiving stations. The receiving stations can be placed at fixedand known locations, such that the approximate location of monitoredpatients can be determined by triangulation,received-signal-strength-indication (RSSI), time-delay of transceived EMsignal, or other means known in the art of real-time location tracking.

In an embodiment, the present invention can be used to identify patientsthat have fallen while attempting to exit a bed or chair. The sensor insuch embodiments can detect sudden accelerations and/or decelerations ofmonitored patient. If the monitoring system of the present inventiondetects a possible patient fall, caregivers can immediately be alertedvia an alarm mechanism.

The sensing system can be used to detect when, and how often, patientsget out of bed. It is common practice to encourage hospitalized patientsto get out of bed frequently. Getting patients out of bed and walkingaround can help prevent hospital-related complications, such as pressureulcers and deep venous thrombosis (blood clots). The sensors describedherein can determine how long a patient is out of bed, how far theytravel, and how fast a patient walks. If a patient is not getting out ofbed or walking sufficiently, caregivers can be alerted via an alarmmechanism. The sensing system can objectively assess a user's level andadequacy of ambulation.

Additional sensing elements for detecting other physiologiccharacteristics can be attached to or incorporated within the sensor 300in addition to the one or more accelerometers and RF units previouslydescribed. One such sensor is a pedometer. This can be used to track thenumber of steps a patient takes or the amount of movement he/she engagesin. The data from the pedometer can be sent in conjunction with the datafrom the accelerometer. As previously mentioned, electrical leads can beincorporated to monitor the heart or other muscle activity. Likewise,capacitive sensors or piezo-electric sensors can be incorporated todetect heart sounds, breathing sounds, or other vibrations. Similarly, apulse oximeter can be incorporated to provide oxygenation data, and atemperature sensor can provide temperature monitoring.

Since the sensor 300 is, in at least some embodiments, powered by abattery or similar device, it is desirable in some embodiments toconserve power. Aspects of the present invention include powermanagement, including burst data transmission, either at regularintervals or in response to a predefined trigger. Portions of the sensorcan be powered down when not needed, including the transceiver,microprocessor, sensors, etc. In an embodiment, the sensors can be usedfor a period, then powered down, and still successfully monitor heartrate and breathing. Capacitive and temperature sensors in someembodiments may need only one reading between power downs.

Low power states can be indicated in a variety of ways, includingflashing, varying intensity on a display, different response wheninterrogated, and transmission of battery information or “I'm alive”information.

As discussed previously, in some embodiments it can be desirable to beable to remove the sensor from the backing affixed to the patient. Insuch circumstances, it is desirable both to ensure that the orientationrelative to the patient is maintained, and also to ensure that the newsensor is secure, an asymmetric relationship between the backing and thesensor can be used, together with any suitable locking mechanism. Inother embodiments, the relationship between the sensor and backing maynot be fixed, but automatically sensed indicators such as electrodes,reflective patches, etc., can be used to inform the system of the newrelative position.

While the foregoing discussion has described an accelerometer-basedsensor in detail, other sensors are also accepted, as discussedpreviously. Thus, referring next to FIGS. 15A-15B and 16A-16B, resistivesensors in accordance with the present invention can be betterappreciated.

In an embodiment of one aspect of the present invention, a supportsurface that contains a plurality of air columns is embedded with anarray of sensors that can detect the presence of surface markers,although a single sensor works in at least some embodiments. Surfacemarkers can be placed on areas of the body that are most susceptible todeveloping pressure sores, such as the hips, heels, and sacrum. Surfacemarkers can also be placed on areas of the body that are resistant todeveloping pressure ulcers. Surface markers can also be incorporatedinto garments, such as socks or underwear. Other wearable items such asbracelets or belts can incorporate surface markers. Surface markers canalso be incorporated into wound dressings, which are then placed overinjured tissue. Specific areas of the user's body can also be demarcatedusing a sensible ink pen. The support surface can be programmed tooptimize surface pressure beneath surface markers. The support surfacecan also be programmed to perform pressure modulating maneuvers at areascorresponding to surface markers. The pressure modulating maneuvers canbe used to encourage blood flow to areas corresponding to surfacemarkers, and can be varied over both space and time. Therapeuticmeasures can also be targeted to areas corresponding to body surfacemarkers. Therapeutic measures can include light therapy (includinginfrared, near-infrared, or low-level laser light), ultrasonic therapy,electromagnetic therapy, or other therapies. Targeting energy (heat) toareas corresponding to body surface markers may cause local blood vesseldilatation, and thus promote blood flow to those specific areas.Therapeutic measures can be derived from within the support surface, orthey can be external to the support surface.

In another embodiment of the present invention, a support surface thatcontains a plurality of air columns is embedded with one or moresensors, such that the perfusion status of the user can be determined atdiscrete locations on their body. The tissue perfusion map generated bythe sensor array can then be used to identify areas of compromisedtissue perfusion. The support surface can use the tissue perfusion mapto optimize pressure distribution and reduce or eliminate surfacepressure at areas identified as having compromised tissue perfusion.Depending upon the implementation, the pressure within one or more aircolumns can automatically decrease at areas correlating to compromisedtissue perfusion, thereby decreasing surface interface pressure at theselocations.

In another embodiment of the present invention, if tissue perfusioncannot be optimized automatically by the support surface, caregivers canbe alerted. Caregivers can then manually optimize the surface pressuredistribution of the patient to prevent tissue damage. With such amethod, caregivers can monitor the perfusion status of a patient. Thesystem can be programmed to automatically alert caregivers of any areasthat register potentially impaired or compromised tissue perfusion.

The support surface can utilize one or more sensors to determine thephysical presence of the user and/or locate specific areas of a user'sbody (which could be demarcated by wound dressings or other surfacemarkers). Depending upon the embodiment, sensors can also be used todetermine the perfusion status, orientation, and other biometric data ofthe user. The sensors can be embedded within the support system, or canbe external to the support system. Depending upon the particularimplementation, types of sensors that can be used in these aspects ofthe present invention include, but are not limited to, resistive,capacitive, inductive and magnetic sensors. Reflective, RFID, infrared,pressure, and stress sensors can also be used in some implementations.Likewise, transcutaneous CO₂ sensors, hydration sensors, pH sensors,ultrasound sensors and remote optical spectroscopy sensors can also beused in certain implementations. Each of these is discussed briefly,below.

Resistive sensors can be used to sense the presence of a user, ordiscrete areas on a user's body, as shown in FIGS. 15A-15B. In thisaspect of the invention, the resistance between two electrodes iscontinuously monitored. The entire user, or discrete areas on a user'sbody, can be covered in a material that has a known resistance. Whenthis material comes into contact with the resistive sensors that areembedded into the support system, a measurable change in resistanceoccurs. This measurable change in resistance can be used to identify thepresence of the user. A computer can be used to synthesize data frommultiple resistive sensors in order to generate a physical location mapof the user. This map can be used to show the location of the entireuser (or discrete parts of the user) in relationship to the supportsystem.

The resistance of the material that is used to cover the user must besufficiently different from the intrinsic resistances sensed by thesensors of the support system when the user, or material worn by theuser, is not present. The intrinsic resistance of the support system canbe due air, bedding, plastic, etc. The resistance of the material thatis used to cover the user can be of lower or higher resistance than theintrinsic resistances sensed.

In one implementation of this method, a sensing system can be designedwith one or more resistive sensors placed across its surface. The userwears clothing embedded with low or high resistance fibers, or a bodysurface marker with low or high resistance properties is placed over aspecific area of the user's body. When the low or high resistancematerial comes into contact with the resistive sensors of the sensingsystem, the resulting increase or decrease in resistance is measurable,and can be used to identify the presence of the user or discrete areasof the user's body.

Multiple different materials with differing resistances can be placed onthe user in some embodiments. With such a method, the materials ofdiffering resistances can be used to demarcate specific areas of theuser's body. For example, if a user had several different wounds, eachwound is covered in a wound dressing that had a different resistance.When the wound dressings come into contact with the sensing system, theresulting changes in resistance can be used to determine the location ofeach wound in relation to the support system of the present invention.Being able to differentiate between different wound sites or differentregions of the body also allows embodiments of the present invention toadapt differently to the different sites. For example, there may bedifferent maximum pressures allowed at each site or different methods ofvarying the pressure at each site. Another usage is to have thematerials of different resistances placed on different parts of theuser's body, which allows embodiments of the present sensing system tolocate and differentiate between different body parts. This can be used,for instance, to improve the mapping of the user with respect to thesupport system. Note that the ability to differentiate between differentregions of interest, and allowing for different actions to be taken oncethe regions are differentiated, can be applied for other sensingmodalities as well that allow for markers that can be differentiable.Here different resistances are used, but different capacitances, RFIDs,and other differentiable markers can be used.

It should be noted that the user does not necessarily need to be coveredin a resistive material in all embodiments of the invention. If theintrinsic resistance sensed by the system in the absence of the user wassufficiently different from the resistance sensed when the user's skinor clothing was in contact with the sensing system, then no specialcovering on the user is necessary. In such a method, the skin orclothing interacts with the resistive touch sensors of the sensingsystem, and causes measurable changes in resistance. A user location mapcan then be generated to identify all locations where skin or clothingwas in contact with the sensing system.

The system can be designed to accommodate for bed sheets, clothing, orother materials potentially intervening between the resistive sensor andthe object to be sensed.

In FIG. 15A, one embodiment of a resistive sensor is shown. Theresistive sensor 1500 is embedded into the support surface 1505 and theresistance between two leads 1510 is measured. The resistance betweenthe leads changes when the patient 1515, or a marker material with adifferent resistance, is placed between the leads. The change inresistance is detected by the resistive sensor, and this information issent to a computer for integration with other sensor data.

In another embodiment, shown in FIGS. 16A-B, resistive sensing can beimplemented in the form of a pad 1600 which incorporates a resistivetouch technology similar to that found in some touch sensitive displays.In such an embodiment, nothing needs be placed against, worn by, orapplied to the patient. In an embodiment, such a pad covers the supportsurface 1605 or can be placed within or beneath the support surface(assuming that pressure due to the presence of a patient is effectivelytransmitted through the support surface) and comprises two resistivelayers 1610 and 1615 vertically separated, such as by an array of smalldots or columns. Pressure from the patient 1620 laying on the padresults in the touching of the two layers, from which the location ofthe applied pressure can be determined. In an alternative arrangement, aplurality of resistive pads can be used, where each pad permits thepressure applied by the patient to be better quantified and resolved.Body parts causing the regions of contact can be identified throughsoftware adapted to recognize pressure distributions, which allows theorientation of the patient to be determined, as well as the magnitude ofthe pressure applied by the various body parts.

An alternative method that can be used to sense the presence of a user,or a discrete area on a user's body, is to use capacitive touch sensors.Here, an electrode can sense the body's capacitance. In such a method,one or more capacitive touch sensors can be used to determine thelocation of the user in relation to the support system. In anembodiment, the user can also wear a material with a known capacitance,which can then be detected by the capacitive touch sensors. Specificareas on the user's body (e.g. wound areas) can also be demarcated usingmaterials with different capacitances. By strategically placingmaterials with differing capacitances over a user's body, a physicallocation map of the user can be generated. When multiple differentmaterials are used (with each having a different capacitance) thecapacitive touch sensors can be used in combination to differentiatebetween discrete areas on the user's body. When used in such a manner,specific areas on a user's body can be “tagged” and surface pressure canbe independently regulated at each tagged location. This is importantfor the management of a user with multiple wounds, where each wound mayhave a different maximum pressure threshold.

Capacitive sensors can be used in a manner similar to resistive sensors,as described above. As with resistive sensors, capacitive sensors neednot be placed against, worn by, or applied to the patient to beeffective. The capacitive sensors can be incorporated into a pad, asdescribed previously. Likewise, multiple body regions can be identifiedand their localized contact pressure can be quantified by measuring thecapacitance resulting from the patient's proximity to the sensor.Depending upon the implementation, one or a plurality of sensors may bedesired.

Inductive sensors can also be used to detect the presence of a user, ordiscrete areas on a user's body. These sensors use an induction loop togenerate a magnetic field. The inductance of the loop can be changed bythe presence or absence of nearby metallic materials, which can beplaced on the user. For example, the user can wear clothing that isembedded with a metallic material, or an adhesive surface marker can beembedded with a metallic material, or a wound dressing can be embeddedwith a metallic material. Materials that have different inductiveproperties can be placed on the user's body at strategic locations. Sucha method allows the inductive sensors to differentiate between differentlocations on the user's body, thereby generating a physical location mapof the user.

Inductive sensors can be used in a manner similar to resistive andcapacitive sensors, as described above.

Magnetic sensors also allow for non-contact sensing, and can utilize amagnetoresistive effect, a Hall effect, magnetic attraction, or anyother means known in the art for measuring magnetic field magnitudeand/or direction. One or more magnetic sensors can be used by thesensing system to detect the presence of magnetic materials in proximityto the support system. Specific areas of the user's body, or the user'sentire body, can be demarcated by wound dressings, surface markers, orclothing that has been embedded with magnetic materials. Specific areasof the user's body, or the user's entire body, can also be demarcatedusing a magnetic ink pen or any other marking capable of beingmagnetically sensed. The sensing system can then detect the magneticfield strength and/or magnetic field direction created by the magneticmaterials to detect the physical presence of a user and/or locatespecific areas on a user's body and/or detect any movement of the userrelative to the support system. The magnetic sensors can measure themagnetic field strength and/or the magnetic field direction producedfrom any magnetic materials placed in proximity to the sensing system.There may be some advantages to measuring magnetic field directionversus magnetic field strength, which include: insensitivity to thetemperature coefficient of the magnet, less sensitivity to shock andvibration, ability to withstand larger variations in the gap between thesensor and the magnet, and the ability to detect angular or linearmovement of magnetic objects. The support system can be programmed suchthat pressure relieving or pressure eliminating maneuvers are performedat or around areas demarcated by magnetic materials placed on the user'sbody. The support system can also be programmed such thatpressurization/depressurization sequences are preformed at or aroundareas demarcated by magnetic materials placed on the user's body. Such amethod can be used to encourage blood flow to specific areas of a user'sbody.

It will be appreciated, from the discussion of resistive, capacitive andinductive sensors, that magnetic sensors can also be placed in a matcovering the support surface, and which has, for example, two layerswhere the applied pressure from the patient moves the layers together ina way that can be measured resistively, capacitively, inductively, ormagnetically, without requiring special clothing or wound dressings orother markers.

A variation of the location markers is that the markers can contain areflective or retroreflective material and a light sensor can detectlight reflected from the marker. The sensor can be located next to alight source, for example an LED. When the marker is positioned in sucha way that the light from the light source reflects back from the markerit can be sensed by the light sensor.

Another variation of the location sensor is using RFID and radiofrequency triangulation. The position can be sensed using RFID by havingsensors with a small and/or directed volume in which the sensors areable to detect the IDs. Having one or more RFID sensors in knownpositions will allow the sensing system to gain information about theRFID tags once they are in the range of the sensors. The RFID tags canbe embedded in body surface markers. An array of sensors on the sensorsystem that detects the RFID tags imbedded in body surface markers andwound dressings is one possible implementation. Alternatively, radiofrequency communication between tags and readers can be used totriangulate the location of the tags.

Infrared (IR) sensors can be used to detect the radiant heat of a userin some embodiments. In one implementation of this approach, a sensingsystem has one or more infrared sensors placed across its surface.Alternatively, the IR sensors can be placed below the surface of thesupport system, where all material between the user and the sensorallows infrared radiation to pass through it sufficiently to obtain anaccurate reading. Alternatively, the IR sensors can be placed externalto the support surface, where there is sufficient line-of-site with theuser. Such a method allows for the remote detection of a user's radiantheat. Thus, infrared sensors can be used to measure the skin surfacetemperature over a large area without directly contacting the skin. Byidentifying all locations within the support system that aretransmitting IR radiation, the physical location of the user relative tothe support system can be determined.

The use of infrared sensors is an established and reliable method forindirectly measuring skin perfusion. Infrared sensing of the user's bodycan provide useful information regarding the temperature of the user atdiscrete locations on their body. Temperature mapping, also known asthermography, can be used to identify locations on the user's body thathave abnormal thermal characteristics. When tissue becomes ischemic,there is a measurable drop in skin surface temperature. Thus, skintemperature is a marker for perfusion, and abnormal changes in skintemperature may indicate perfusion abnormalities within tissues. Boththe absolute temperature of the skin, and temperature changes over time(ΔT) can be used as markers for perfusion abnormalities. To determinethe ΔT at discrete areas on the user's body, the thermal map of the usermust be correlated to a physical location map of the user. Correlationof the physical location map of the user with other biometric data canbe performed in the manner previously described. Since skin temperaturevariations are known to correlate with perfusion abnormalities,interface pressure can automatically be relieved at areas registeringabnormal temperatures. Such a method can be used to optimize the user'sperfusion status. Infrared sensors can comprise a two-dimensional arrayof discrete sensors such as semiconductor photodiodes, bolometricdetectors, or other temperature sensors known in the art. Alternatively,a thermal imaging camera having a CCD or other two dimensional imagingsensor can also be used.

Pressure sensors can be used to detect both the physical presence of theuser, and indicate areas of potentially compromised tissue perfusion. Assurface interface pressure increases, the probability of compromisingtissue perfusion also increases. Sustained surface pressures above 32mmHg have been shown to correlate with impaired blood flow, and thusgreatly increasing the risk of tissue necrosis.

Pressure sensors can be used in conjunction with other sensors tooptimize pressure distribution over the entire support system.

The critical interface pressure threshold may vary between differentlocations on the user's body. For example, areas corresponding towounded tissue may not tolerate any surface pressure. Tissues overlyingbony prominences may have relatively low surface pressure thresholds.Tissues overlying thick layers of fat or muscle may tolerate relativelyhigh surface pressures. To assign different surface pressure thresholdsto specific locations on the user's body, the sensing system needs to beable to correlate user position and surface pressure data. Furtherdescription on how to correlate the physical location map of the userwith other biometric data is contained herein.

In an embodiment, the pressure distribution map of a user can also beanalyzed to determine the position/orientation of said user relative tothe support surface. In such a fashion, the pressure at distinct regionsof the patient's body can be determined.

A stress sensor can be used in some embodiments to measure the stressapplied to the support surface due to the pressure created by the user'sbody. Some examples of stress sensors are strain gauges orpiezoresistors or resistive fabrics/threads that change resistance uponstretching. Stress sensors can be placed on the surface of the sensingsystem, or within the walls of the sensing system. The stress sensorscan also be placed in a sheet or mat that overlies the support surface.The stress sensors will stretch or compress as a function of theexternally applied pressure due to the user's body weight. The stresssensors can also be placed directly on the user's body to measure skinstretch or compression. In addition to estimating pressure, the stresssensors can be used to gather data about shear stress. The data from thestress sensors can be used both to determine the physical location ofthe patient and to help identify areas of potentially compromisedperfusion due to increased pressure or shear forces.

Transcutaneous oxygen pressure (TcPO₂) sensors can be used in someembodiments both to detect the physical presence of the user and toindicate areas of potentially compromised tissue perfusion. The TcPO₂ isa noninvasive method for assessing the perfusion status of a user. TheTcPO₂ is related to the degree of ischemia, with decreasing oxygenpressures indicating areas of compromised tissue perfusion. The TcPO₂ isconsidered to be a sensitive and reliable determinant of a user'sperfusion status.

TcPO₂ sensors can be placed on the patient or on the support surface.The transcutaneous oxygen pressure can also be measured remotely, asdescribed later in this document.

Similarly, transcutaneous carbon dioxide pressure (TcPCO₂) sensors canbe used in an embodiment both to detect the physical presence of theuser and to indicate areas of potentially compromised tissue perfusion.TcPCO₂ monitors offer a non-invasive method of continuously measuringcarbon dioxide tension. The TcPCO₂ is related to the degree of ischemia,with increasing carbon dioxide pressures indicating areas of compromisedtissue perfusion

TcPCO₂ sensors can be placed on the patient or on the support surface.

In an embodiment, hydration sensors can be used both to detect thephysical presence of the user and to indicate areas of potentiallycompromised tissue perfusion. The assessment of tissue hydration can beused to detect dehydrated or edematous tissue. The hydration status canalso be measured remotely, as described. later in this document.

The pH at discrete locations on the user's body can be detected remotelyusing a near-infrared light sensor in some embodiments. This techniquecan be used to accurately detect small changes in the pH of subcutaneoustissues. This technology works by detecting the difference in absorbancebetween protonated and unprotonated molecules. As tissue becomesischemic, the acid content increases, and the ratio of protonated tounprotonated molecules increases. Thus, an increase in protonatedmolecules correlates with impaired perfusion, and the support system canautomatically offload pressure at areas identified as having impairedperfusion.

Ultrasound can be used in some embodiments as a sensing modality togather physiologic data from the user. This data can be used alone, orin combination with other sensing modalities, to assess the perfusionstatus of a patient at discrete locations on their body. Dopplerultrasound can also be used to assess blood flow. If areas of abnormalperfusion are detected, the support system can automatically optimizesurface interface pressure at those locations, and caregivers can bealerted. Pressure optimizing maneuvers performed by the support systemcan be used to promote blood flow to critical areas.

In some embodiments, tissue oxygen tension, carbon dioxide tension, pHand hydration status can be analyzed remotely using near-infraredoptical spectroscopy. The skin is a relatively weak absorber ofnear-infrared light, so near-infrared spectroscopy can be used toanalyze the epidermis and dermis. Near-infrared spectroscopy can be usedto examine spatial and temporal changes in tissue hemodynamics and canprovide pre-clinical detection of perfusion abnormalities. Whenperfusion abnormalities are detected, the support system of the presentinvention can automatically redistribute pressure away from areas ofcompromised tissue perfusion.

Hemoglobin has distinct absorption bands in the near-infrared spectrum,depending on whether the heme group is oxygenated or deoxygenated. Whentissue is exposed to near-infrared light, the chromophores within thetissue (such as oxygenated and deoxygenated hemoglobin) will absorblight at distinct wavelengths. Thus, the light that is ultimatelyreflected off of the tissue will contain wavelengths of light that werenot absorbed by the chromophores. Oxygenated hemoglobin absorbsnear-infrared light strongly in the 900-950 nm range, while deoxygenatedhemoglobin absorbs near-infrared light strongly in the 650-750 nm range.

Water is the major component in tissue, and it absorbs near-infraredlight most strongly at wavelengths above 900 nm. The absorptioncharacteristics of water are distinct from hemoglobin, so water can beanalyzed independently of hemoglobin. Therefore, in some embodiments,near-infrared spectroscopy can provide information regarding tissuehemodynamics, in addition to information regarding tissue hydration andwater content. Such a method also allows for the detection ofsubclinical edema or swelling.

With the use of near-infrared spectroscopy, as shown in FIGS. 17A and17B, a perfusion map of the patient can be created. One or morenear-infrared light sources 1700 are used to analyze multiplephysiologic processes such as TcO2, pH, and temperature. One or moreinfrared sensitive cameras 1705 can be used, placed sufficientlyproximate to but separate from the light sources so as to receivereflected light from the patient without receiving bleed-over from thelight sources. The support system then optimizes surface pressure basedon the tissue perfusion map. The support system can use the data fromthe perfusion map to automatically optimize surface pressuredistribution and alert nursing staff or caregivers of any potentialabnormalities. Surface interface pressure can essentially be eliminatedat areas that are identified as having compromised tissue perfusion orsigns of tissue injury. In addition to helping patients with decubitusulcers, the present invention can be useful in the treatment of patientswith burns, chronic wounds, skin grafts, flaps, and other injuries.

Laser Doppler Flowmetry can also be used for measuring perfusion incutaneous microcirculation in some embodiments. The technique works byilluminating the tissue of interest with light from a low-power laser.The beam of laser light is scattered within the tissue of interest andsome of the light is scattered back to a sensor. Most of the light isscattered by static (non-moving) tissue, but a certain percentage of thelight is scattered by moving red blood cells. The light scattered bymoving red blood cells is distinct from the light scattered by statictissue (i.e. it has a unique oscillation frequency), so the oscillationfrequency of the backscattered light correlates with the relative numberand speed of moving red blood cells. Thus, this technique can be used tomeasure the relative amount of moving red blood cells and measure theiraverage velocity. This technique is completely non-invasive and can beused to interrogate subcutaneous tissue to a depth of severalmillimeters. If areas of abnormal perfusion are detected, the supportsystem can automatically eliminate surface interface pressure at thoselocations, and caregivers can be alerted. Pressure relieving maneuversperformed by the support system can be used to promote blood flow.

In some embodiments, it is desirable to combine perfusion data frommultiple sensing modalities to increase the specificity of the detectionsystem and thereby improve the ability to detect ischemia. The falsepositive rate can be decreased if the perfusion map is generated fromthe synthesis of data from multiple sources. For example, if thetranscutaneous oxygen tension is determined to be low at position X, butthe pH is normal, the temperature is normal, and the Laser Doppler Flowis normal at position X, then this can be considered a false positivetranscutaneous oxygen tension measurement at position X and the supportsystem will take no action. However, if multiple sensing modalitiesindicate that perfusion is compromised at position X, then the supportsystem can immediately perform pressure relieving maneuvers at positionX and can alert caregivers. The minimum number and/or type of sensingmodalities that are required to initiate pressure-relieving maneuverscan be predefined by the user or caregivers. A weighted mean can beconstructed using data from the different sensing modalities, where theweight of each sensing modality is determined by its importance,reliability, and effectiveness in detecting tissue ischemia.

In some embodiments, it is desirable to correlate perfusion data withposition data to better address areas of compromised perfusion on thepatient. Perfusion sensors can be used to determine if certain areas ofthe body are at risk of ischemic damage or are in the early/late stagesof ischemic damage. The support system can be designed to dynamicallymodulate surface interface pressures, so as to promote adequate bloodflow to target tissues. When the support system addresses areas ofcompromised perfusion, it is helpful to correlate the ischemic area withan actual physical location on the user. The methods by which this canbe done will vary depending on whether the perfusion sensors areembedded in the support system or adhered to the patient's body.

In an embodiment, the support system can have one or more sensors acrossits surface. These sensors can be used to identify potentially ischemicareas. In order to determine what part of the body correlates with apotentially ischemic area, the system needs a reference frame to knownparts of the body. Here, reference markers can be placed on the body inknown reference locations such as the elbows, knees, ankles, wrists,spine, hip, etc. These reference markers can be sensed by the systemusing a number of potential modalities (e.g. capacitive, inductive,resistive, magnetic, RFID, etc). These reference markers can be used todemarcate known body landmarks. Each reference marker can also haveunique sensible qualities (e.g. differing capacitance, resistance,inductiveness, etc.) such that the support system can distinguishbetween the different reference markers and thus identify the differentbody landmarks. In such a method, the system can know, for example, ifit's sensing a reference marker for the elbow vs. the wrist. If themarkers are not unique or differing, the support system can use therelative locations of the reference markers, in conjunction withinformation about the known shape of the user and possible orientationsof the user's body to estimate the location and orientation of the userin relation to the support system. Alternatively, the support system cantake the data from the sensors embedded within it to determine whichsensors in the array are sensing the presence of the user and use thatdata, along with the data about the user's shape/size/possible motions,to make an estimate of the user's orientation and location in relationto the support surface. For example, a pressure map which is generatedfrom a support surface that contains pressure sensors, can be used toestimate the user's location and orientation. The same principlesdescribed here for pressure sensors can be applied for most or allsensing modalities.

Referring next to FIG. 19, in an embodiment the user's position,location, and orientation relative to the support surface is estimated.A model of the body with range of motion and weight is created. This canbe generic or it can include data specific to the user. The body model,in combination with the sensor data is used to generate the locationmap.

In some embodiments, sensors such as perfusion sensors are placeddirectly on the patient's body. These sensors can determine, forinstance, if any areas on the user's body are ischemic. Perfusionsensors can employ a number of different sensing modalities (e.g.transcutaneous oxygen pressure, skin temperature, etc.). This biometricinformation, along with positional information obtained via knownreference markers, can be relayed to the sensing system. In addition toinformation regarding the user's perfusion status, the reference markersplaced on the user can also have unique identifiers (e.g. differingcapacitance, resistance, RFID, etc). The perfusion sensors can thus bejuxtaposed with known reference markers, so as to link perfusion andposition data. Perfusion sensors and reference/location markers can beplaced in close proximity to each other, or with a known relationship toeach other, so as to create a close link between perfusion and positiondata. Knowledge of the specific location of each perfusion sensor inrelationship to the support system can be used to generate a tissueperfusion map of the user. The sensing system can be responsible forsensing both the perfusion sensors and the location markers, thusallowing the sensors and markers to be smaller and less complex.

The transmission of sensor data from the user to the support system isimportant in some embodiments of the present invention. Perfusionsensors can detect a multitude of different physiologic factors that aremarkers of ischemia. If these sensors are located on the user, thesesensors must be able to relay that information to the support system.One method of accomplishing this is to have wires linking the sensors onthe user's body to the support system. The sensors can also be designedto wirelessly transmit information. Another method of accomplishing thisis to have the perfusion sensors induce sensible changes in anindicator. The indicator is located on the user, and the indicator canbe incorporated into the sensor itself. The changes within the indicatorcan then be sensed by the support system. For example, the perfusionsensors may induce a change in the capacitance or resistance of anindicator. This change in capacitance or resistance can be sensed by thesystem. Therefore, the system will be able to indirectly receiveinformation relating to the perfusion status of the user.

Sensors can be placed over the entire body surface, or they can bestrategically placed at areas that are at high-risk for becomingischemic, such as the hip bones, tailbone, heels, ankles, and elbows.Strategically placing sensors only at high-risk areas may reduce thetime required to prepare a user for perfusion sensing. Sensors can alsobe strategically placed at locations with a known physical relationshipto a high-risk area, but not directly on the high-risk area. Using fewersensors may also reduce the total sensor bandwidth, while not greatlyreducing efficacy.

To aid in the placement of the sensors, an adhesive sheet with an arrayof embedded sensors can be placed on the user. The sheet has printedthereon clear landmarks, so as to aid in the proper placement of thesensor array. For example, in an embodiment the sheet has printedlandmarks that are designed to correlate with anatomic landmarks, suchas the L4 vertebral prominence, the ASIS, the trochanters, etc. Thesesheets can come in different sizes to accommodate different shapes andsizes of users. These sheets can also be designed to stretch toaccommodate different sizes and shapes of users. These sheets can alsobe translucent, transparent, breathable, reusable, and/or removableafter sensors are properly placed, leaving the sensors in place. Thismethod of using a “sheet” of sensors can greatly increase the speed,ease, and reliability with which the sensors are placed. Sheets can bemade with the features described above to conform to any body part andcan also be designed to accommodate a wide range of potential sensorarrays. The sensors can also be embedded in form-fitting socks,undergarments, gloves, patches, and sleeves.

In FIG. 18, a sheet 1800 with sensors 1805 having anatomical landmarksis shown. Such a method allows for the quick and easy placement ofsensors at the hip and tail bones. It should be noted that the sensorsused in the present invention can be found in many locations andorientations. Possible sensor locations include, but are not limited to,embedded in the support surface, embedded in a sheet that overlays thesupport surface, or positioned beneath or around the support surface.

In many embodiments of the invention, it is desirable to optimizepressure at areas corresponding to body surface markers. The presentinvention utilizes a novel method for eliminating interface pressure atareas corresponding to wound dressings or other body surface markers.One method of accomplishing this is to embed wound dressings or bodysurface markers with a material that can be sensed by the system. Thesensing system can then track the location of all wound dressings andbody surface markers, and optimize surface pressure accordingly. Thus,interface pressure can be reduced or eliminated beneath wounds and otherhigh-risk areas. There are many ways to make sensible wound dressingsand body surface markers, a few of which are described herein.

In an aspect of the invention, wound dressings capable of being sensedby a remote host through either a wired or wireless connection are used.Such sensible wound dressings can also comprise body surface markers2000 and 2005, such as depicted in FIG. 20. These wound dressings andsurface markers can be composed of an adhesive material, such that theycan be applied to a patient's skin. The sensing system can thenautomatically identify the presence of a wound dressing or surfacemarker, and then perform pressure optimizing maneuvers at those specificlocations. As the patient moves in relation to the support system, thesensing system can continually track any wound dressings or surfacemarkers that are in proximity to the surface of the sensing system.

In some embodiments of the invention, it is desirable to incorporatesurface markers into clothing worn by the patient. The surface markersused in the present invention can be incorporated into form-fittingclothing, such as socks, undergarments, gloves, patches, bracelets, orsleeves.

In FIG. 21 a sock 2100 is shown which has been embedded with one or moresensible materials. The sensible materials can be embedded at specificlocations of the sock, such as the heel, lateral malleolus and/or medialmalleolus. The user can wear the sock, and when the sock is placed inproximity to the surface of the sensing system, pressure optimizingmaneuvers can be performed at that specific location. As the patientmoves in relation to the support system, the sensing system cancontinually track any socks that are in proximity to the surface of thesupport system. Note: socks or sleeves can be made to conform to anybody surface, such as the arm or leg. Also, specialized sleeves can bedesigned to fit over specific “at risk” areas, such as a tissue graft orflap.

Also in FIG. 21, an undergarment 2105 is shown which has been embeddedwith one or more sensible materials. The sensible materials can beembedded at specific locations, such as the hips, and sacrum. The usercan wear the undergarment, and when the undergarment it is placed inproximity to the top surface of the support system, pressure optimizingmaneuvers can be performed at that specific location. As the patientmoves in relation to the support system, the sensing system cancontinually track the undergarment, as long as it remains in proximityto the surface of the support system. The undergarment should remain ina fixed position relative to the patient, such that any movement of theundergarment directly reflects movement of the patient.

In an aspect of the invention, magnets 2200 can be implemented to createsensible body surface markers, as shown in FIG. 22. One method ofcreating sensible wound dressings and body surface markers 2205 is toembed these items with a flexible, soft, and magnetically receptivematerial. The magnetically receptive wound dressing then interacts withsmall magnets, or electromagnets, that are contained within each of thesupport surface's air columns 2210. When the magnetically receptivewound dressing is put in proximity to the support surface, the magnetscontained within the support surface are attracted towards the wounddressing. Each air column comprises a force sensor that can measure themagnitude of the magnetic attraction. The support surface then respondsby decreasing the air pressure in those air columns that register a highforce. As the registered force increases, the air pressure within thecorresponding columns decreases by a proportional amount. Thus,interface pressure is relieved or eliminated under areas that havemagnetically receptive dressings. In another embodiment, the supportsurface contains an array of magnetic sensors positioned at somedistance beneath the top layer of the support surface. This magneticsensor array can be used to determine the coordinates of magnetic bodysurface markers placed within proximity to the sensor array. Thelocation data can be communicated with the support surface, which thenoptimizes surface pressure or delivers targeted therapy based on thisinformation.

FIG. 22 depicts a method for eliminating surface pressure beneath woundsusing such magnets. A dressing that contains a magnetically receptivematerial is used to cover any wound or tissue. The sensing systemcontains small magnets that are attracted to this magnetically receptivewound dressing when the two are placed in proximity. The resultingmagnetic force will be sensed by the system, and air pressure within thecorresponding air columns will be decreased.

Another method that utilizes magnets is to have magnetic sensorsembedded in the support surface. The surface markers can be made of amagnetic material which can be easily recognized by one or more magneticsensors embedded in the sensing system. Magnetic sensors are relativelycheap, highly sensitive, and allow for non-contact sensing. Non-contactsensing is advantageous because the user will not have to “feel” thesensors, which could be uncomfortable. A specific area of a subject'sbody can be demarcated using a wound dressing, body surface marker, oreven clothing (i.e. sock, underwear, glove, etc.) that has been embeddedwith a magnetic material. Or, a specific area of a subject's body can bemarked out using a magnetic ink pen. The sensing system can then detectthe magnetic field strength and/or magnetic field direction created bythe magnetic materials to: 1) detect the physical presence of our testsubject, 2) locate specific areas on our test subject's body, 3) detectany movement of our test subject relative to the support system, 4)optimize interface pressure beneath the magnetic surface marker. Themagnetic sensors can be used to measure the magnetic field strengthand/or the magnetic field direction produced from any magnetic surfacemarkers placed in proximity to the support system. There may be someadvantages to measuring magnetic field direction versus magnetic fieldstrength, which include: insensitivity to the temperature coefficient ofthe magnet, less sensitivity to shock and vibration, ability towithstand large variations in the distance between the sensor and themagnet, and the ability to detect angular or linear movement of magneticobjects.

The sensing system of the present invention can also utilize a fabricthat can conduct electricity. Body surface markers can then be placed onthe patient, such that when they come into contact with the sensingsystem there is a measurable change in resistance. Using this method,the sensing system can track body surface markers on the patient andregulate surface pressure accordingly.

Similarly, conductive thread can be interspersed with normal fabric toadd conductivity to a fabric or material. This can allow normal fabric,paper, or plastic materials to become conductive (or have lowerresistance) while maintaining, for the most part, their otherproperties.

To prevent undesirable interference with other treatment or patientmanagement regimens, fuses that limit the amount of current that canpass through the conductors in the sensing device can be placed in thesensor sheet. They can be placed, for example in series with conductorsin contact with the bed or patient. If for instance, defibrillators areto be used on the patient, the fuses can be used to reduce the flow ofcurrent along the conductors.

These fuses can be separate from the conductors, but can also take theform of segments of the conductors. In either implementation, only apredetermined maximum current is permitted to flow through them beforethey break the circuit. In at least some embodiments, high valueresistors can be used to limit current to levels which present no dangerto either the patient or other equipment in the vicinity.

An alarm function can be incorporated into the sensing system. If thesensing system determines that a particular region of the body (asdefined by body surface markers) has been experiencing sub-optimalperfusion for an extended period of time, then caregivers can be alertedvia an audible or visual alarm. The alarm can be transmitted wirelesslyto a nursing station.

The sensing system of the present invention can utilize one, some or allof the sensors described in this document to identify areas ofcompromised tissue perfusion. The support system can then optimizesurface pressure in order to restore blood flow to under-perfused areas.

Any of the above concepts, sensors, and devices can be applied for useon a chair, wheel chair, operating table, or any other support surface.

In an embodiment, pressure sensors are embedded into the surface of theoperating room table. The pressure sensors are used to generate apressure map of the operative patient. If any area registers a highpressure for an extended amount of time, an alarm will sound. Then, thepatient the patient's position can be adjusted so that the pressure isrelieved.

A system can be designed where a sheet of pressure sensors is securelyplaced over the surface of the operating table prior to the operation.Alternatively, a sheet composed of a pressure sensitive fabric can alsobe used. The sheet may be disposable.

When the sensing system detects areas of compromised tissue perfusion ortissue injury, interface pressure can be eliminated at those specificlocations. Stated differently, pressure at specific locations on thepatient's body can be offloaded in some embodiments of the presentinvention. The support system can be designed to relieve pressure aroundspecific locations in a gradual fashion. Such gradual pressureoffloading prevents sudden and dramatic changes in interface pressure.Dramatic pressure changes can lead to, amongst other things, poorcirculation or a feeling of “dropping out” of the support system. Themagnitude of the pressure gradient can be adjusted and the minimuminterface pressure can be set. The rate of pressure offloading can alsobe adjusted. The rate of pressure offloading per unit distance from agiven location can be defined by the user or caregivers. The rate ofpressure offloading over time can be defined by the user or caregivers.These adjustments can be made to maximize comfort or to optimize thedepressurization at and around target areas.

In FIG. 23, certain areas requiring pressure relief are marked(indicated by the ovals). In the case of a single marker 2300, interfacepressure is gradually reduced and the pressure is lowest directlybeneath the marker. When multiple markers 2305-2310 surround an areathat requires pressure relief, the pressure is gradually decreased andthe pressure is lowest within the region cordoned off by the markers ata computed optimal location.

The support system can be designed in some embodiments such that itallows for sequential increases or decreases in interface pressure atspecific locations. Such sequential pressurization and depressurizationcan be used to promote blood flow to selected tissues. In oneimplementation of this method, a support surface that contains aplurality of air columns is embedded with an array of sensors, such thatthe perfusion status of the user can be determined at discretelocations. The individual air columns can regulate their air pressure inorder to optimize blood flow to target tissues. The dynamic air pressurechanges can be designed to follow certain patterns that are known tofacilitate blood flow, such as having pulses or waves of pressure moveradially towards or away from target tissues. Other modes of pressurechange are also possible.

In FIG. 24, different patterns of pressure change are shown. The dottedlines show local maxima of pressure that shift as indicated by the thickarrows. Shown here are expanding rings of pressure 2400, rotating radiallines of pressure 2405, and lines of pressure moving in one direction2410. Also shown is the pressure at high risk areas being lowered oreliminated using any given pattern of pressure change.

In addition to varying the maximum pressure of an alternating pressuresupport system, other features can be modulated. These include, for anylocation along the support system, the minimum pressure, the frequencyof pressure changes (including a frequency of 0 Hz, i.e. no pressurechange), the duration of high pressure (or duty cycle), the amplitudechange, the maximum and minimum amplitude, and the rate at whichpressure changes occur. Location sensing of body surface markers canallow for these variations in pressure optimization to be targeted tospecific areas on the body. One example of this is for the head to bedemarcated, such that surface pressure at this location remainsrelatively or absolutely constant, so as to allow for a stable headsupport.

In some embodiments, the support surfaces and devices described in thisdocument can employ learning algorithms that determine which pressureoptimization techniques work best for each individual patient. Thealgorithms can take into account perfusion data from sensors that isacquired before, during, and after different pressure optimizationmaneuvers are performed. The effectiveness of the different pressureoptimization maneuvers is recorded and assessed to determine whichmaneuvers, or of combination of maneuvers work best for an individualpatient. Though this can be effective for any user, those users whospend more time on the support surface will benefit most from having apressure optimization protocol that is more robust and customized basedon their specific physiologic parameters. Though perfusion is onemeasure that can be optimized by the learning algorithm, other measurescan also be optimized using the learning algorithm.

Certain locations on the body are especially susceptible to developingulcers, such as the hip bones, tailbone, heels, ankles, and elbows.Areas at high-risk for developing ulcers can be demarcated using bodysurface markers that are applied using an adhesive sheet, as shown inFIG. 18. The lower image shows a more detailed view of the adhesivesheet that is used to apply multiple body surface markers both quicklyand also in the correct orientation with respect to the patient and eachother.

In these locations, the pressure is often concentrated over bonyprominences. The use of cushioning and supportive materials at thesesites can distributes pressure over a larger area, thus relievingpressure over bony prominences. The use of such devices can help preventulceration and aid in the healing of wounds and ulcers.

One common problem with such devices is that pressure is relieved athigh-risk locations whileby transferring pressure to other sites,thereby increasing the risk of ulceration at these other sites. Twoimprovements are described herein: 1) utilizing a gradient ofdepressurization and 2) having the support cushion perform dynamicpressure optimization maneuvers.

A currently available cushion and supportive device that fits on theheel is often used to help relieve pressure on the heel. Whereas thepressure can be easily distributed in the case of a heel or elbow (giventheir low mass), the improvements mentioned above can allow cushions andsupportive materials to be used at heavily loaded areas, such as the hipand tailbone.

FIG. 27 shows the pressure adjustments in one embodiment for a supportsurface 2700. The pressure is reduced at the high-risk area 2705, andthere is no dramatic pressure differential between the edges of adjacentcolumns 2710 of the cushion. The resulting pressure drop is gradual.This method of gradual pressure redistribution can be used to optimizeperfusion at high-risk areas while also improving patient comfort.

The pressure gradient can be adjusted and customized for each specificuser, body part, or wound site. Discrete areas of individuallycontrolled pressure exist in the cushion. The pressure at discrete areaswithin the cushion can be independently regulated by adding/subtractinga substance from these areas. This substance can be a soft solidmaterial such as foam; a fluid such as water; or a gas such as air.

In addition to a pressure gradient, the cushion/support device can alsocreate shifting/or dynamically changing pressures. In one instance, thiscan be accomplished by having the pressure within the individualchambers of the cushion controlled by a pump or other air pressurizationdevice. The pressures can then be automatically adjusted and modulatedover time. The pressure changes can follow selected patterns tofacilitate blood flow, such as having pulses of pressure that moveradially away or towards the side of risk or damage. Similarly, thepulses or waves of pressure can fan out from the area of risk and/ormove around it. Other modes of pressure change are also possible.

In FIG. 25, different patterns of pressure change in a cushion areshown. The dotted lines show local maxima of pressure that shift asindicated by the thick arrows. Here shown are expanding rings ofpressure 2500 and rotating radial lines of pressure 2505. Also shown isthe pressure at the areas of risk being lowered or eliminated with anygiven pattern of pressure change.

These same techniques can be applied to the heel and elbow and otherareas of the body as well.

The support cushion described above can be designed to accommodate anyor all of the sensing mechanisms described in this document. Byincorporating perfusion sensors into the support cushion, thehemodynamics of the target tissue can be monitored and pressure can beoptimized to facilitate blood flow. Any of the concepts, sensors, anddevices mentioned in this document can be used in conjunction with thesupport cushion.

Using the concepts and sensors described in this document, sleeves,patches, or dressings can be designed that monitor the perfusion statusof a user at any location on their body (not just tissue that is incontact with the support system). If abnormal perfusion is detected, analarm can be used to alert caregivers. Such devices can be particularlyuseful in monitoring the perfusion of a tissue graft or flap.

An arrangement of air columns in different orientations is one variationof a support surface that allows for fine two-dimensional control ofsurface pressure with fewer air columns required.

Shown in FIG. 26 is a support surface with two layers of horizontal aircolumns 2600-2605 that are arranged perpendicular to each other.

If only a column on the top layer deflates, the rows in the bottom layerwill expand as their pressure is higher than the top layer such that thearea covered by the deflated top layer column is supported by the bottomlayer rows. The top layer columns and bottom layer rows are arrangedperpendicular to each other. If only a bottom layer row is deflated, thetop layer column expands such that the area covered by the bottom layerrow is supported by the top layer column. If a top layer column and abottom layer row are both deflated, then the only area not fullysupported by both top and bottom layers corresponds to the area wherethe deflated column and row intersect. Thus, modulating the pressure inboth rows and columns allows surface pressure to be controlled atspecific locations.

The devices and methods of the present inventions have a variety ofother applications. For example, the support system can be designed tominimize shear forces or regulate temperature or adjust humidity. Thereare also applications outside of the treatment of wounds. For example,the sensing system can be utilized by patients with diseases such asCystic Fibrosis, where they require localized chest percussion therapy(CPT) at regular intervals. More specifically, embodiments of thepresent invention for creating variable pressure patterns can be used tocreate an automated percussion protocol that optimizes the expulsion ofmucus in patients with Cystic Fibrosis. The same principle can be usedin other applications where percussion therapy can be of benefit. Otherpotential applications of the present invention are described brieflyherein.

The ability to detect shear forces directly and to eliminate themimproves the treatment and prevention of wounds and pressure ulcers. Onemethod to detect shear forces is to place shear sensors, such as straingauges or piezeoresistive sensors, at the interface of the skin and thesupport surface. In one implementation, the shear sensors can beimbedded at or just beneath the surface of the support surface. Theshear sensors can also be placed in a sheet that is placed on top of thesupport surface. The shear sensors can also be attached directly to theskin. These shear sensors can be used to sense a force that causes astretch or compression in directions that are tangential to the surfaceof the skin.

Another approach is to use conductive fabric or threads that changeresistance based on their stretch. Measuring changes in resistance canbe used to quantify stretch in the surface which can be correlated toshear forces. Shear forces can be estimated by knowing the orientationof the patient and/or the position of the support surface on which thepatient is lying or sitting.

Once a shear force is detected, a number of actions can be taken,depending upon the embodiment. One or more shear sensors can form a mapof the shear forces at different locations along the support surface oron the skin of the user. The areas experiencing highest shear forces canbe highlighted to alert the user or caregiver to reposition the user toreduce shear forces. A map of shear forces along the support surface oron the skin of the user can be generated to monitor shear forces.

In addition to detecting shear forces, embodiments of the supportsurface can be used to automatically eliminate excess shear forces. Oncea shear force above a certain threshold is detected, the support surfacedetermines the location where the force is generated. A method similarto that discussed above for correlating perfusion sensor data withpatient position can be used for sensor data localization, where shearsensors are used instead of perfusion sensors. The support surface canthen adjust the interface pressure at and around the location of theshear force, so as to relieve the shear force.

One method of automatically eliminating shear forces involves increasingpressure at areas surrounding the area of increased shear force, andthen reducing the pressure at the area of increased shear force, untilsufficient pressure is relieved such that the skin/tissue and supportsurface may move/slide relative to each other.

In order to prevent excessive frictional forces, the reduction inpressure can be fast and allow for complete elimination of pressure.Such a method allows for relative motion of the skin and support surfacewithout contact. The pressure changes that aim to reduce shear forcescan be temporary, so as to allow the support system to quickly reacquirethe optimal resting pressure conditions.

The pressure changes created by an embodiment of the invention that aimto reduce shear forces can employ moving pressure waves, rings ofpressure reduction, or alternating areas of increased/decreasedpressure. The optimal method of shear force reduction can depend on thesize, shape, and fragility of each specific skin area.

The support system can incorporate a feature in which a sufficientlyhigh shear force must be present for a certain amount of time before anyaction is taken. Such a method can help eliminate actions triggered bytransient and self-limited increases in shear forces.

The user, perhaps due to sensory deficits, may not be able to feel shearforces and therefore may not be able to adjust their positionaccordingly. In the present invention, shear forces can be monitored andautomatically eliminated. The user and/or caregiver can be alerted ifshear forces cannot be automatically eliminated by the support surface.

When the shear force sensors are not placed directly on the skin, butare instead placed, for instance, in the support surface, some of theshear forces detected may not be transferred to the skin. Instead thesedetected shear forces may be due to pressure and the natural stretch ofthe material in which the sensor is imbedded. Since the shear forceexperienced by the skin is the measurement of interest, it is useful todetermine which forces measured are most likely transferred to the skin.One method to do this is to correlate a shear force sensing map with apressure sensing map. Where the pressure is sufficient and likely to beresponsible for a given sensed shear force, this shear force reading canbe ignored or subtracted. The remaining shear forces can be assumed tobe more likely to be transferred to the skin. This method can becustomized to varying degrees by allowing adjustable levels of ignoring,subtracting, or weighting of data from shear forces sensors.

Moisture and temperature regulation can also be important in theprevention and treatment of wounds. For moisture it is important to keepareas of uninjured skin dry in order to avoid maceration. For wounds, itmay be important to keep these areas moist and to not let them dry out.The humidity of the air surrounding the skin and the presence of fluidscan be detected by the sensing system. Humidity sensors and fluidsensors can be placed on the skin or in the support surface. Wound areascan be demarcated, and areas that have suboptimal moisture levels,whether too wet or too dry, can be detected. For areas with excessmoisture, the support surface can act to reduce moisture. For instance,the permeability of the support surface can be changed. The supportsurface can have water channels that open and allow for fluid to drain,be wicked away, or be suctioned out. The support surface can also allowfor gas to be blown in and exit, so as to allow for moisture toevaporate. The support surface can reduce the pressure at a certain areato allow for gas to flow between the skin and the support surface. Inareas with insufficient moisture, the moisture reduction methods can bestopped or moist gas can be delivered to the area of reduced moisture.

Temperature regulation is important for wound prevention and treatment.Temperature regulation is a problem particularly for users with impairedbody temperature regulation. Individuals with a spinal cord injury (SCI)may have difficulty maintaining a constant body temperature, with lossof reflex sweating or regulation of blood flow. For temperature sensing,several methods exist, including thermisters, radiant heat detection,and IR sensors. Once an area of suboptimal temperature is detected, thesupport surface can act to correct the temperature. Several methods canbe used for temperature control including, but not limited to: pumpingheated or cooled liquids or gas near the surface of the support surface;pumping gas between the skin and support surface to encourage heat lossby evaporation; using thermoelectric heating and cooling elements; usingelectric heating elements; and alerting the user or caregivers of thesuboptimal temperature, so that action can promptly be taken.

The support surface can optimize the surface temperature at discretelocations on the user's body. It is known that heat delivered tospecific regions of the body, such as the back, can have a relaxing andtherapeutic effect. Since the sensing system of the present inventioncan identify specific locations on a user's body, heat can be deliveredto a user at specific locations. Similarly, cooling can be delivered toany part of the body. The sensing system can determine the location ofthese specific body locations, either by generating a physical locationmap of the user or by employing markers on the user's body. If bodysurface markers are used, multiple unique body surfacemarkers can beapplied to specific areas of the body, such that the temperature at eachbody surface marker can be different. Heating and cooling cycles andprotocols can also be employed.

In some embodiments, knowing the position of the user and being able tochange, sufficiently, the pressure across the support system at specificlocations allows for automatic rolling of users. For example, if usersare lying on their back, pressure can be increased on one side of theirbody while pressure is simultaneously being decreased on the other side,effectively causing or encouraging a roll. This can be extremelybeneficial for patients who are prone to developing pressure ulcers, andshould be rolled frequently. This can also be useful, for instance, forusers with sleep apnea or snoring problems who may experience fewersleep disturbances while sleeping on their side. In such a situation,the support surface can detect when a user is in an unfavorable positionand can roll them accordingly. The system can detect when a sufficientroll has been achieved, at which point the surface pressure may revertback to its normal state.

For patients with CHF, the support system can adjust to tilt the patient(head up and feet down) to decrease strain on the heart. This can beused in conjunction with a pulse oximeter, or other sensors, to detectsmall changes in blood oxygenation.

With the use of body surface makers, the system can identify bodysurface regions corresponding to the lung fields and deliver percussionor vibration therapy directly to those locations. Percussion andvibration therapy can also be delivered in a specific pattern withrespect to the lung fields in order to maximize expectoration ofrespiratory mucus and debris. Pulmonary therapy delivered in this mannermay aid in keeping the lungs clear.

The inventions and devices described in this document can also bedesigned for use by the general consumer population. One implementationfor the general consumer is a device that generates a physical locationmap of a user's body and then optimizes surface pressure for thepurposes of enhancing ergonomics. This allows the support system toautomatically and dynamically customize ergonomics for each specificuser and in response to the user's current position and specificproblem. Such technology benefits those who have back problems whorequire, for instance, specific lumber support. The sensing system isable to identify the lumbar region of the user, and optimize surfacepressure to support the lumbar region. Furthermore, the support systemin such an embodiment is able to adjust pressure across its surface toallow the user to rest in a neutral, ergonomic, and healthy position.

In another aspect of the invention, an embodiment of the sensor 300configured to detects sleep cycles can be used with the system of FIG. 1to enable the sensing system to be able to function as an alarm clock.It is beneficial to be awoken at a specific stage in the sleep cycle(i.e. immediately after REM sleep). The sensing system can determinewhat stage of the sleep cycle a user is in by either directly measuringthe EEG or by indirectly monitoring other biometric data (such asmovement, because people are paralyzed during REM) in the manner taughthereinabove. The user is then awakened at the optimal time via anysensory stimuli (visual, auditory, olfactory, touch) appropriate to thatpatient. The support system can also regulate surface pressure toencourage the patient to exit the support system at the desired time.The patient can designate a time range in which they would like to beawoken. The system can then identify the best time within this range towake the patient.

In another aspect of the invention, the operating table can have apressure sensing mat across its surface. The mat can be embedded intothe operating table, or can be securely wrapped across the surface ofthe support system (like a bed sheet). A pressure map of the patient canthen be generated. If areas of high pressure are noted for greater thanone hour, or other predefined amount of time, then the caregiver isalerted. Since patients are typically paralyzed when on the operatingtable, they should not be moving, and there is no need to correlateposition and pressure maps. An LCD display associated with the pressuresensors can be used to indicate where the area of high pressure islocated in relation to the operating table.

Pressure sensing pads can be used to monitor pressure between body partsor between body parts and other objects. For example, between the knees,between elbows/wrists and the side of the body. When the patient islying on the side or when the arms are bound close these areas canexperience high pressures as well. The pressure mats can be shaped andformed to help stay in place and also help to pad these areas.Caregivers can be alerted if sustained periods high pressure aremeasured.

Because the sensing system can determine the exact position of thepatient relative to the support system, the support system can be usedto aid in rapid airway management by automatically positioning thepatient in an orientation that facilitates intubation. For example, theneck can be forced to protrude, so as to increase glottic exposure. Thehead of the bed can be elevated, so as to decrease the work of breathing(obese patients can sometimes have difficulty breathing while lyingflat). Elevating the head of the bed can also be useful for patientswith sleep apnea or congestive heart failure, where a vital signsmonitor can be used to determine the appropriate incline level (as therespiratory rate increases or oxygen saturation decreases, the level ofincline increases).

In another aspect of the invention, the maximum size of an acceptable“indentation” in the support surface can be predefined, so as to preventthe user from falling into a hole created in the support system. Havinga maximum limit can be important when treating patients with largewounds. Smaller areas of reduced pressure can migrate under the woundarea, so as to minimize pressure over a large space for periods of time.

It will also be appreciated that, while the foregoing primarilydiscusses support surfaces for hospitals and nursing homes, thetechnology of the present invention has broader potential applications.For example, the technology can be utilized in the home or car. Forexample, a wallet in the back pocket can be a nuisance when driving. Awallet can be embedded with or contain a sensible material. Then,whenever the user's wallet is placed in proximity to the seat of the caror wheelchair or other support surface, a small indentation isautomatically created at the location corresponding to the wallet. Thisallows the patient to sit comfortably in the seat of their car, withouthaving to remove their wallet from their back pocket. This method neednot be confined to wallets, and instead is appropriate for any objectsclose to the body that create discomfort or increase the risk ofpressure ulcer formation.

This document focuses on the use of “air columns” as the basis of thesupport system. It should be noted that air columns are not required inall embodiments. Any support system that can regulate its surfacepressure at discrete locations can be used. Other methods include, butare not limited to: hydraulic systems, columns of bubbling sand andmechanical pistons.

Having fully described a preferred embodiment of the invention, andnumerous aspects thereof, as well as various alternatives, those skilledin the art will recognize, given the teachings herein, that numerousalternatives and equivalents exist which do not depart from theinvention. It is therefore intended that the invention not be limited bythe foregoing description, but only by the appended claims.

We claim:
 1. A method for automatically determining the status of awearable sensor device, the method comprising: affixing the sensordevice to a user, the sensor including at least one accelerometer,generating, by the at least one accelerometer of the sensor device,acceleration data indicating an acceleration of the sensor device in atleast one axis, determining, by a processor, acceleration-basedbiometric data regarding the user based at least on the accelerationdata generated by the at least one accelerometer, the acceleration-basedbiometric data including at least one of acceleration-based respiratorydata, acceleration-based cardiac data, or acceleration-based bodymovement data, comparing, by the processor, (a) the acceleration-basedbiometric data of the user to (b) reference biometric data stored in adata storage device associated with the processor, identifying, by theprocessor, based on the comparison of the acceleration-based biometricdata of the user with the reference biometric data, a sensor deviceattachment condition associated with the sensor device being notproperly affixed to the user, and in response to identifying the sensordevice attachment condition, automatically outputting ahuman-perceptible alert notification via a display or other outputdevice.
 2. The method of claim 1 wherein the acceleration-basedbiometric data includes at least one of a respiratory rate, a heartrate, or a pulse rate.
 3. The method of claim 1, comprising determiningan angular orientation of the sensor device with respect to the userbased on the acceleration data generated by the at least oneaccelerometer.
 4. The method of claim 1, comprising determining alocation on the user's body at which the sensor device is affixed basedon the acceleration data generated by the at least one accelerometer. 5.The method of claim 1, wherein comparing the acceleration-basedbiometric data of the user with reference biometric data comprisescomparing the acceleration-based biometric data of the user with apredetermined range of biometric data values.
 6. The method of claim 1,wherein the wearable sensor device includes visible indicia indicatingan orientation direction for aligning the sensor device with respect tothe user.
 7. The method of claim 1, wherein: comparing (a) theacceleration-based biometric data of the user to (b) reference biometricdata stored in a data storage device associated with the processorcomprises comparing (a) the acceleration-based biometric data of theuser to (b) at least one reference biometric data threshold value, andidentifying a sensor device attachment condition based on the comparisonof the acceleration-based biometric data of the user with the referencebiometric data comprises determining that acceleration-based biometricdata exceeds the at least one reference biometric data threshold value.8. The method of claim 1, wherein: comparing (a) the acceleration-basedbiometric data of the user to (b) reference biometric data stored in adata storage device associated with the processor comprises comparing(a) the acceleration-based biometric data of the user to (b) a referencebiometric data range of limit values, and identifying a sensor deviceattachment condition based on the comparison of the acceleration-basedbiometric data of the user with the reference biometric data comprisesdetermining that acceleration-based biometric data falls outside thereference biometric data range of limit values.
 9. The method of claim1, further comprising: monitoring, by the processor, based on theacceleration data generated by the at least one accelerometer, anorientation of the user over time; identifying, by the processor, anorientation alert condition based on the monitored orientation of theuser; and in response to identifying the orientation alert condition,automatically generating and communicating a human-perceptible alertnotification regarding the orientation of the user.
 10. The method ofclaim 9, wherein: monitoring an orientation of the user over timecomprises monitoring the orientation of the user with respect to a turnprotocol for the user; and automatically generating and communicatingturn notifications based on the monitored orientation of the user withrespect to the turn protocol.
 11. The method of claim 1, whereincomparing the acceleration-based biometric data of the user withreference biometric data comprises comparing the acceleration-basedbiometric data of the user with previously generated and storedacceleration-based biometric data of the user.
 12. The method of claim11, wherein identifying a sensor device attachment condition based onthe comparison of the acceleration-based biometric data of the user withthe reference biometric data comprises determining that a differencebetween the acceleration-based biometric data and the previouslygenerated and stored acceleration-based biometric data of the userexceeds a defined threshold.
 13. A system, comprising: a wearable sensordevice configured to be affixed to a person or to an article worn by theperson; at least one accelerometer provided in the wearable sensordevice and configured to generate acceleration data indicatingaccelerations of the sensor device in at least one direction; aprocessor communicatively coupled to the at least one accelerometer; anda data storage device associated with the processor and storingreference biometric data; wherein the processor is configured to:determine acceleration-based biometric data regarding the user based atleast on acceleration data received from the at least one accelerometer,the acceleration-based biometric data including at least one ofacceleration-based respiratory data, acceleration-based cardiac data, oracceleration-based body movement data; compare the acceleration-basedbiometric data of the user to the reference biometric data stored in thedata storage device; identify, based on the comparison of theacceleration-based biometric data of the user with the referencebiometric data, a sensor device attachment condition associated with thesensor device being not properly affixed to the user, and in response toidentifying the sensor device attachment condition, automatically causea human-perceptible alert notification to be output via a display orother output device.
 14. The system of claim 13, wherein theacceleration-based biometric data includes at least one of a respiratoryrate, a heart rate, or a pulse rate.
 15. The system of claim 13, whereinthe processor is configured to determine a location on the user's bodyat which the sensor device is affixed, or an angular orientation of thesensor device with respect to the user, based on the acceleration datagenerated by the at least one accelerometer.
 16. The system of claim 13,wherein comparing the acceleration-based biometric data of the user withreference biometric data comprises comparing the acceleration-basedbiometric data of the user with a predetermined range of biometric datavalues.
 17. The system of claim 13, wherein the processor and the datestorage device are provided in the wearable sensor device.
 18. Thesystem of claim 13, wherein comparing the acceleration-based biometricdata of the user with reference biometric data comprises comparing theacceleration-based biometric data of the user with previously generatedand stored acceleration-based biometric data of the user.
 19. The systemof claim 18, wherein identifying a sensor device attachment conditionbased on the comparison of the acceleration-based biometric data of theuser with the reference biometric data comprises determining that adifference between the acceleration-based biometric data and thepreviously generated and stored acceleration-based biometric data of theuser exceeds a defined threshold.